As for the timings sucking at 2000? They really don't, to be perfectly honest. Keep in mind that timings are rated in clock cycles, so 8 cycles at 1600MHz is the same latency as 10 cycles at 2000MHz. Therefore, DDR3-1600-8-8-8-24 is identical in latency to DDR3-2000-10-10-10-30 (and if you have deep enough pockets, you can get DDR3-2000-7-7-7-20, which is lower latency than DDR3-1600-6-6-6-18). I still don't think 2000 is worth it, but that's a cost issue, not a latency issue.
There is not much of a difference.
But one solid reason for getting DDR3 is that they will be supported by new proccy and mobo.
They will last longer.
But if you already have 4+Gb of DDR2 then I don't see a point of upgrading just ram.