Edit: I seriously spend like, 1 or 2 and a half hours typing this all. Wow.
Never really cared it.
I'm neatural to it personally but also dislike it. Megan McCathy said in a interview that she HATES Sparity and Dislestia so I highly doubt both of them will ever become cannon.
Spike orginially feel heads over heels with Rarity mainly for her psychical appearance. He's pretty much marveling at her looks in the very first episode (Rarity is the prettiest of the Mane Six though you gotta admit with the prettiest character design!)
Sure, Spike has matured a bit in Inspirtion Masfesion (or however you spell it), Simple Ways, and especially Secret To My Excess.
And we kinda see some development between the two. With Spike comforting her and seeing a bit of Rarity's personality and inner beauty but the shipping and Spike's affections towards Rarity are mostly based upon the outer beauty of Rarity and Spike constantly admires Rarity's looks rather than admire more for her personality.
And Rarity's appearance is the orgin of the crush.
We do see Spike and Rarity bonding sharing tender moments with each other and Spike really has matured in season 4 a bit.
Especially in Inspirtion Masfesion and Simple Ways. He isn't whiny or depressd with heartbreak in the slightest over Rarity fangirling over Trender Poop Hoof. And he comforts Spike and almost companions her in the episode.
I was pretty surprised by Spike's maturity in that scene actually.
Also in Inspirtion Masfesion with Spike comforting Rarity acting even more maturely. We also see Spike struggle with a inner conflict in himself to tell Rarity the truth of his opinion on Rarity's actions. Good development I suppose.
And Secret To My Excess was good too. Spike is willingly giving away a birthday gift for himself for the pony that took his heart
(pun not intended)
and is happy that Rarity is happy. Which matters most to him.is her happiness due to his little puppy crush.
And the ending of course remembering that moment between him, Rarity, and that kiss.
All in all, the shipping has some good development and pontenial. Except Megan's hatred of course.
But a lot of people tend to complain Rarity taking the heart gem was Rarity taking advantage of Spike's generousity which it does somewhat feels like (and this is coming from a Rarity fan!)
With other episodes people feel she takes advantages from him. I kinda disagree in a few ways. Why would Rarity do that anyways? She seems somehow unaware of his affections and attraction to her. So can't see how and if she found out about the crush, she'd most likely be both slightly flattered and a bit in shock at the same time.
As for other Spike ships...
2) SpikeBelle:
Not all SpikeBelle shippers agree on the whole "Go for the sister dude!" trope. Take me a for example: I DOWNRIGHT BLOODY DESPISE that cliche' in SpikeBelle fanwork.
As for AppleSpike, (I prefer SpikeJack so it's not mixed with good old Applebloom. ) like I said, they have some good and decent moments of interaction in a few episodes here and there at times.
You can even imagine them off-screen. A good moment between them I can recall is in the ending and aftermath of the Ticket Master.
I somewhat agree on the other ships being crack-shippings. Some of the other Spike X Mane Six however have good moments of bonding. Except the show's focus is on Sparity. However, it's like the phrase;
"Beauty is in the eye of the beholder".
In this case it's "Shipping Chemstrity and Moments are in the eye of the beholder" or something like that.
We can use our imaginations and potray the ships anyway we wish to. And a lot of fanworks like fan-fiction as key examples could make almost any shipping work. And like said, Spike has great moments between the other Mane Six besides Rarity like Twilight for example. Though I agree we could clasify and consider them as crack-ships.
1) Spikebelle: Cute idea. Sadly only interaction is that moment in a Canterlot Wedding. Plus, I like to point out it's tradionial for a ring boy to dance with a flower girl. Then again it's interesting they use Sweetie Belle, Rarity's own little sister, instead of Applebloom and Scootaloo. (I despise SpikeBloom anyways so eh ) Not to mention they both have similar personalitles. Both can be kinda dorky or goofy at times, can mess things up and annoy everypony around them (Spike can quite annoy Twilight and we see Sweetie constantly get on Rarity's nerves though they later get cool with it), both are thought to be less than everyone else as Sweetie is looked down upon with the other Crusaders for being a blank-flank and a complete dorky goof who can mess up easily which can describe Spike as he tries to prove everyone around him wrong that he's better than their expectations. Which Sweetie Belle constantly tries to do mostly for getting her Cutie Mark and using everypony she's great with theater work in For Whom the Sweetie Belle Toils.
Also: http://www.fimfiction.net/group/198085/spikebelle/thread/166504/spoiler-alert-anyone-else-think-season-5-episode-1-was-a-great-oppertunity-to-add-spikebelle-into-the-show
^^^^THIS. The words taken right out of my horse mouth. (Pun not intended, once again.)
The shipping is more potrayed with Sweetie as the one hitting on Spike while Spike is busy marveling and daydreaming of impossible adventures of saving his fair lady princess Rarity.
Rather unfortunate for those who do use the other potrayal of "Can't get the hot/cute girl? Go for the sister!"
I want to rip that apart so badly. And very unlikely. Spike would most likely if rejected go depressed for a bit and eat a lot of ice cream like he did in one episode when he felt sad or depressed. Can't quite recall. Or sleep in bed all day.
Then later schemeing up a plan to win Rarity's affections over like Senpai Notice Me or something.
Sweetie developing some kind of crush on Spike would be more likely and fit more perfectly in the show rather than Spike noticing Sweetie Belle first.
---------------------------------------------
Done with SpikeBelle.
As for my opinion on a certain apple and dragon:
2) SpikeJack: Not bad. Like I've mentioned before: we see some moments between them in the series. In the Ticket Master we see him at the end all giddy over his ticket so Applejack all smug-like and acting like They actually have good interaction. Especially the ending of Spike At Your Service. Despite being a bad episode, there are a few moments like when Applejack just saved Spike from the timberwolves and at the end which was good interaction and bonding. They also seem to have other moments in other episodes we don't really notice that could be off-screen too. Not to mention the little blushing moment between them in Spike At Your Service near the end.