Would i have much to gain by installing a stock replacement K&N air filter? I saw a pretty convincing K&N square filter demonstration at a farmshow last month.

The $145 at PPF or $200 at DP for true intakes is a bit much for me.

You won't get much. The biggest part of an intake is the box/tubing/piping. If you look at yours, it goes in the tube, accross AND through the filter (2 ways) and then through the rough rubber tubing.

Get some pipe bent @ a local shop, or check out my thread in this board, on modifying a pipe I got at autozone.

At the very least, do what I did to my stock airbox with the drop in K&N. It'* still not quite as much as a custom intake, but it comes close, and it'* less than 20 bucks, plus the cost of the filter:

Yes I know True CAI Kits are $$$$$
I modified my own Stock air box to accomidate a ram air setup.
See here: http://www.cardomain.com/memberpage/250343/4
I used 4" black duct to accomplish a ram air tube that picked up air from the front fascia near the LH driving light.

I have a gutted air box and K&N flat filter and found it much better over stock. Since the smaller pulley and headers install the filter it starting to 'cup' in the center so a cai is the next mod for me.