While I'm okay with the lower tiers dropping off (really I think this should only begin at very high levels), I'd like to get back to the possibility of TDs giving some increase in monster difficulty, or stats, or HP, in addition to the levels in this thread.
The monster level increase from TDs creates more of a challenge, that's why I go down trapdoors. Really, I'm looking for more of a challenge that still allows some chance of finding drops (even if the increase in drop rate is marginal compared to a massive increase in difficulty, I think it would add depth to the game). I went to level 143 or 144 on my magician last season and the challenge was a lot of fun, but drops were abysmal, so many would consider that "pointless" and in some sense I guess I did too, because I stopped leveling that character.
I don't think there is a major cause for concern with newer players not having good enough gear to go down trapdoors when they are adding something like 5-10% monster stats and 1-5 monster levels per trapdoor, since we have had events with 25+ monster stats before and drops were slightly better but good items have been dropping without any monster stats/difficulty/quality event too. I think monster stats would be a good balance, but I would also be fine with a much smaller value for a much more effective monster mod per trapdoor (something like 1-5% monster difficulty per trapdoor would make the game way more fun to me).
Anyway, please don't give up on this idea!