Downrez to help performance?
 

I'm getting ready to edit a large project with over 30 hours of raw footage with Aspect HD in Premiere Pro 2. The native resolution of my footage is 1440x1080, but I'm thinking of downrezing everything to 1280x720 with HDLink to help editing performance in Premiere. Will this in any way have an effect?

The stress on the decoder will obviously be reduced, but what spec is your PC? Just about any modern dual core system should be able to handle the specs of your footage with much aplomb.

The fact that you're going progressive on a progressive system is good.
1280x720 will be easier on the system and you could do more layers, or see less render bars.
If you're final output is SD, then you're still editing with higher quality.
You might take a hit in longer encode times on the front end, as I believe the m2t file is captured to a temp file, then it's convert and scaled (in your case) to 720p avi.

Do a small test. Capture a tape at with 1280x720p scaling and compare.

I have a dualcore system with 2 gigs of ram, but I've experienced skipping in both video and audio while playing back the timeline when I have many elements in the project file and on the timeline. On smaller projects things work without a hitch.