I forget what brand mine is, but I have black tape over about 90% of the red lens on the front of the thing. Still, it picks up every flash you see and many more you don't see.... such that you might as well let the camera go ahead and just fire away and not use the trigger at all. I got tired of messing with it, but I asume you could cover the thing over with more and more tape till it only picked up actually visible bolts.
You would only want to use a trigger for daylight lightning, and if you could get it adjusted just right, using one might be worth it.
Dan had some good points earlier in the thread.
With an active storm you can get right up under the thing where it is a bit darker, set your fstop to somewhere around 16 or so, and just let the camera shoot continuously at whatever exposure you want. I've got two picture of the same bolt this way before, shooting with a rebel XT. You will have to delete a lot of pictures, but you will get some good close ones too. Also you can get some by just reacting to the bolt. You won't get the nice branched stuff that way though. Anymore I am always trying to put myself right in the CGs trying for a super close one at 10mm.
But keep messing around with the trigger and maybe you will get it set up right.
Oh and I don't know about the filters you asked about, I just haven't gotten into any of the specialized stuff.... but I'm assuming if you had a filter that only reduced the amount of light and didn't screw up the scene in some way, that would be a good thing in really bright conditions. I'm just not sure how it would effect the look of the bolt itself.