I don't believe the introduction of the 500R will bring down the resale value of our 250R's at all - certainly not any more than the new 2013 250R's will..
I'm not saying $4K isn't a good chunk of change, but when we're talking trade-in values of around $3K for a used 250 that originally cost $4K - we're not talking a huge loss here gang. We also can't factor in after-market upgrades for dealer trades (only if you're selling privately).
No matter what you buy, as soon as you drive / ride away off the dealer lot, just chop off 20%-25% of what you just paid on day 1. If you can't live with that loss and it's not worth upgrading to a bigger & faster machine, just keep what you have & enjoy the he*l out of it.