There are upscalers you could buy and just keep your 3805, although the cost of some of these scalers is more than some of the new receivers. Unless your TV is capable of 1080P there is no reason to move up to HDMI as the 720P/1080i signal is carried on component cables, which your 3805 has a single output to your TV.

Here is a thread(long) on the subject of 720 vs 1080.

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70