I doubt your going to get a general consensus, as you see from the posts there are a lot of opinions.
However, facts have already been posted. The stock TBI itself is a restriction. No matter how much air you try to get into it, IT is the restriction. Increase it's size, and air intake might help. Whether stock intake routing flows enough for the TBI, probably no hard data (flow tests) but I think anyone that looks at it will say that stock is pretty close to as much as the TBI will flow. Scientific eh?
I know that GM used a weird piece on the core support to get air from. I haven't seen enough of these trucks to see if that's standard, or just in some applications. Most carbed apps simply take air from the front of the core support, no other way for air to get in. So it is truly cold air. The last TBI truck I saw had openings BEHIND the core support as well as through the core support. (IIRC some diesels had those too) This obviously would not all be cold air, so theoretically not as good as the carb versions in that respect.
If yours is like the above one I described, if you can find a way to block off those other openings, then you have probably helped somewhat. At least enough to make you think that you've done some good. Not meant in a derogatory way, simply that you've attempted something and no clue if it actually does something beneficial. Theoretically yes, in practice?