If we're discussing electric guitars here, then the amp should be your first consideration when 'it's time to move up'. To get really great tone, you need to pay careful attention to all of your gear, but I think the key element is the amp. That may sound strange coming from someone who has 11 guitars, and 3 amps, but the fact is; I can appreciate the differences in my guitars because I have some great amps. A bad-sounding amp is going to sound bad regardless of what guitar you plug into it.