This probably should've been first, but anyway.
I've said before, and meant it, that if I wanted to make a 'serious' Bloodlines mod, the last engine I would want to use is Bloodlines. I know some restrictions can be circumvented, but it's still a PITA all around, with a plot that can only be spun so many different ways before you're actually changing the game.
Personally, I would go with Dragon Age 1. As long as the mod is non-commercial, you're pretty much golden. I'd still rather see you go off and make a real commercial game from scratch though - I can recommend a few good engines (C4 tops my list). You're way too good to stick around as a modder. 'Indies' can make money in this industry if they keep their scope realistic.
Back to DA1:
1) A lot of Bloodlines 'charm' is the cutscenes. Dragon Age was designed specifically to do double duty as a mechanime generator - meaning you can make all the cut scenes you want, with lip syncing and voice overs and anything else you wanted, without having to pull teeth and and workaround engine limitations all day long.
2) Scripting - almost everything that can be pulled out of the engine has been. All the combat code, equipment, character, npc, and 'monster' stats - that's all scripted and can be completely changed to work however you want it. You could do an absolutely 'by the book' PC version of the tabletop combat rules if you wanted, though some things are probably best modified a bit for the medium.
3) Ease of creation: You can make new cities, wilderness, roads, towns, interiors - pretty much anything you want. Will it look totally modern if you stick to stock resources? No - but you could do a helluva game set in Scotland...