I've got 5 cards; one empty PCI. The one beside the vid card is empty. Here are the cards: (recently dead) SB128 digital, 1394 card, IOMagic PCPVR capture/tuning card, 10/100 lan card, 56k v.92 modem. Quite a lot. I don't think that many slots are necessary though because newer boards have integrated features, and you need to use a case spot for the brackets anyway.
Setup once 8rda+ arrives tomorrow: SPDIF header, PCPVR card, v.92 modem, USB2 header, 1394 header, gameport header. That'll be 6 slots taken by only 2 cards and 4 headers.
Cliffs notes: no, extra pci's won't help. You can place headers in case openings to get desired functionality, and the header prevents the pci slot from being used anyway.