I've been through this dilemma as well, as I only started playing a few years ago. My thoughts:
- A good amp with a lousy guitar trumps a good guitar with a lousy amp (I went from a Silvertone 5W practice amp to a Peavey Classic 30 - like night and day!).
- You have an MIM Deluxe Strat - these are good guitars. If you had a bullet Strat (which aren't even that bad, IMHO), I might have recommended upgrading that. But your guitar is good.
- The best thing is practice. At the beginning, I was frustrated, and assumed that all the cat and ferret noises coming from my amplifier were a result of the guitar and the amp. So I bought my Classic 30. But much of it was due to fretting too hard (sharpening the notes), poor picking technique, accidentally muting due to poor left-hand technique, and so on. I can't stress what a huge difference I saw after taking private lessons with a great teacher. He corrected my technique, and I began improving far faster than if I had gone it alone. Now, I can sound decent with that little Silvertone, even if I do sound better after switching to the Classic 30. I'm never satisfied with how I play, and have so much to learn, but when I step back and think of what I can play now, and how much I know, I really have come a long way.
- (and the only way to do that is with practice, not plastic.)
I love Vox amps. Get the AC15, and play the hell out of it. And if you can afford it, look at some lessons with a good teacher, too.
EDIT: I see you already have a Super Champ. Those are great. My advice: don't sell it - keep it, save up your money, and then buy the AC 15.
Yup...true. Need more practice!