I would march straight to the immigration counters and see how they are. If they are horrendous (likely these days) then I'd probably not bother and would kick around lounge hopping in BKK.

However, if they are not too bad I would go into town for sure. If you are lucky enough to get through sharpish then you could be in town within 30 minutes.

As for what to do then, you've got a multitude of choices. This is Bangkok we're talking about, and if you can't find anything of interest there you really shouldn't be allowed to travel.