7.0 Classic/TBC lootgold

No changes. Only interesting for Legendary/Pet/Enchanting material farming.

Classic
http://bit.ly/29roIE3    //    1g26s65c  Skeram as a quick example. Gold doesn't matter in Vanilla. All these bosses have been through                                                several nerfs (5.0.4 + before).

TBC (25man)

http://bit.ly/29CeXUM    //   10g  TBC standard
Bosses still drop 10g with a few exceptions (no changes also):
http://bit.ly/29DTBsD    //    1g  Maulgar (#1 Gruul, unrelated nerfs in 5.0.4 and before)
http://bit.ly/29m3mHC    //   20g12s76c  Magtheridon, no real change
other exceptions:
Kael'Thas, Vashj, Twins, Muru, KJ, Archi, Illidan.
These Bosses always dropped a bit more. Nowadays ranging between 12g and 14g.

Other reasons to "farm" TBC (or old content in general): Enchanting Tomes that unlock Transmog appearances for old weapon enchants. Void Crystalls (1-2 per epic) (and other old ench. mat.) might skyrocket for a short time.