I also had a Lian-Li and that dust filter does an incredible job. I only have the original fans on there and I can clean that filter every week (I had a very dusty environment - it's better now). I also have very little dust inside now, all because of that filter.

And I agree, definitely replace the PSU. Besides, it's a good thing to upgrade, especially now that components are requiring so much more power (thanks NVidia). I never really worry about power with my Antec. It's also pretty quiet. I'd definitely recommend their line.