The X360 has quite a few years left, muff. If Microsoft wants to make any money this generation, they have to keep it awhile.
Not only this, MS spokespeople have already said the next X360 is still 4-5 YEARS away still. They saw what the PS2 is still doing, and are hoping the X360 comes to the same way. They've even said they will make games for the X360 when the next system comes out ala Sony and God of War 2.
It's totally your call if you want to wait or not. The X360 might get a price drop (or I should say that it's more than likely) when GTAIV comes out. If your willing to wait, you could save yourself $50 by waiting. However, the game library is totally awesome, and you might end up like many X360 owners, and if you don't get it now, you'll be backlogged on many, many fantastic games.
If you get a X360 now, or later, do some smart shopping and make sure you pick up a Falcon unit. Check the power supply. If it's 175w, you know your getting a Falcon. Every report I've seen has shown that the Falcon has fixed any and all RROD problems. They're a thing of the past for the Falcon units. So feel free to buy with confidence.