The iPhone is due around 22nd June, the iTouch 4G is likely not to arrive until Sep or Oct but it may be worth waiting until June to see what improved hardware features the 4th iPhone has as it will probably make its way into the iTouch as well later.
The most likely new feature of both the iPhone and iTouch is a higher resolution screen, with 960x640 (double in both dimensions compared to the current 480x320) being a possibility.
Whilst there may well be a lower spec cheap iTouch model included in the 4th gen range, I would expect that lowest spec model in the autumn would not be the existing 2nd gen hardware 8GB version, but a 3rd gen model with at least 16GB of storage (flash memory prices are constantly falling, as is the other hardware).