Apple *ALWAYS* has something new and cool "just around the corner."
"Just around the corner" is the dumbest phrase ever coined, as it can mean anything.
Given that iMacs are (broadly speaking) refreshed yearly, you're always (by law of averages) about six months or so away from the next refresh. You could spend the rest of your life (literally) waiting to catch the "perfect" moment. It will never actually come.
Buy a computer when you need a computer. Buy the best one you can afford, make sensible add-on purchases (like maxing out the RAM when RAM is cheap, buy an external drive for backups etc), take the few modest steps necessary to maintain your Mac and keep it running smoothly, and stop trying to win the rat race.
This is the way to get years of solid enjoyment out of your investment. The best part? After several years of great computing, you'll see something from Apple that is such a marked improvement on what you have that it's compelling enough to buy -- at exactly the time you were thinking of retiring your old workhorse!
