newer guns are nicer, but if your gun works there is no NEED to buy a new one, only the WANT factor.
I sold my SL8R because i don't travel with a team any more, and thus don't play much. So I'm building a timmy just for pick up games or if i decide i want to practice with friends or local teams if asked to fill in.
The things you're missing out on would be things such as, thinner frames (no clamshell), lighter guns, no macro line, and they easier to disassemble. But your gun will still shoot smooth if tuned, and with the virtue you can still shoot 12.5 easy.