Cold air drafts coming through recessed lights ( assuming they are mounted in an insulated ceiling area ) are an insulation issue .. not an electrical issue. Unfortunately aside from crawling in a packing more insulation around the VB bag, i don't think there is a whole lot more you can do.
You DON'T want to pack insulation right up against the fixture as it could cause either overheating, bulb failure, lamp shut down from temperature sensor, or in worst case .. a fire.
Most of the decent insulators that i know will usually encase the unit in batt insulation before blowing the insulation into the rest of the attic space.
As for the inaccessible fixtures? A couple of suggestion are:
- If you can get a small hand sized access hole near them perhaps some expanding spray foam can be sprayed in to help. (Not being an insulator , my suggestion is only that .. a suggestion ... i would check with a professional first.)
- You can try removing the fixture from below ( not an easy task .. and likely to cause significant drywall damage depending upon how the fixture is mounted ). If this can be done you can cut the VB bag from below, pack in more insulation as best you can, re-seal the VB bag, and re-mount the fixture.
