Your metaphor only works for dinner parties. And then only for small ones.
Campaigning to be Leader of the Free World requires enormous organizational and financial planning, and as such, it asks people to assume risk. People are asked to commit.
The only other conservatives that will get in at this point with the organizational or fund raising capability, even this far out, have to be either Governors or Gingrich, and may be General Franks. Rice or Powell, not interested.
Its amazing that Senators even bother. People can't stand them, and they don't have the executive experience that people are looking for in a President. Senators are much more followers than they are leaders. Leaders run for executive offices, retired lawyers run for representative office.
The Pubbies damn well better find somebody. Giuliani will lose in McGovernesque numbers.