I suspect I may have a very slightly bent front fork.  I keep adjusting them, but the right side seems to always end up about a millimeter or two higher at the top then the left one. 

If it's bent (how would I tell for sure?), it's been bent for about 9 months of riding.

What should I do about this?  Will I regret ignoring it? Is it worth replacing the forks?  If it is, should I replace them with GS forks, or upgrade to something 'better', and if so, what?  I have already done the progressive spring upgrade.

Thanks!

How are you adjusting them - describe your process...

Having the forks end up at different height in the triples does not strike me as symptomatic of bent.

Bent or not - how to tell - jack up the front of the bike, pull the wheel, undo the triples, pull the forks, place a straightedge on the exposed fork tubes, rotate and check again - if bent, you should see it as not straight.

You would also notice binding as the pair of forks move up and down, installed.

Another fork check, installed, is to hoist the front of the bike (to get as much fork as is going to show to show) and place a flat surface (sheet of glass works well, or you can use a hairy eyeball if you have a good one) against the exposed forks (sight across if using the hairy eyeball). They should be perfectly flat against the surface - this shows up "system assembly" problems like twist as well as bends or the like.