The factions were definitely what made Sigil interesting. I also liked how the natives thought they were cosmopolitan because the universe passed through their portals, but they were actually the most parochial douche bags in all the planes. I hope they don't keep the Victorian slang and the Dickensian London flavour text for 4e though, which was lame.
As for buying books in general, I definitely prioritize my purchases to 1) minis 2) adventures, 3) flavour text books like Manual of the Planes. For rulebooks, I'll probably pick up the Monster Manuals only, because those are the books I like reading. For creating characters, I like the character builder better.
If I didn't have a character builder, I probably would have bought Arcane Power and PHB2, but I would have bought less minis, and I wouldn't have finally manage to buy P1. (I lost my chance to buy H3 because I waited too long).
As for buying books in general, I definitely prioritize my purchases to 1) minis 2) adventures, 3) flavour text books like Manual of the Planes. For rulebooks, I'll probably pick up the Monster Manuals only, because those are the books I like reading. For creating characters, I like the character builder better.
If I didn't have a character builder, I probably would have bought Arcane Power and PHB2, but I would have bought less minis, and I wouldn't have finally manage to buy P1. (I lost my chance to buy H3 because I waited too long).