I had laser eye-surgery after getting a 3DS, and I can't say I remember the 3DS screen appearing any different when I had glasses than it does now. So I don't see what difference glasses make.
Anyway, I say wait. £60 (maybe less) extra for a system that is much more ergonomically-pleasing. Bigger screens, and so much more comfortable to hold. Also, the battery life is better on the XL. Still not as good as I'd like, but considering how terrible it is on the 3DS, any step in the right direction is appreciated. In the long run, it will be well worth it.