You don't need multiple IPv4 addresses to make use of a wild-card (or other multi-name) certificate. A wildcard certificate will verify any matching domain so you could have many sub-domains of the same domain (using a single certificate for *.domain.tld) on one address and browsers would not complain.

Also you could run the distinct (sub)domains on different ports on the same address, though this is perhaps less useful.

Also, with SNI you can use many single-name certificates on one address (and all on the same port) using SNI. Unfortunately there are a number of significant client combinations that won't play nice with this (most notably, if you can't guess, IE on Windows XP): http://en.wikipedia.org/wiki/Server_Name_Indication#Support