With respect (really), citing Mail as the good guy and outlook as the bad guy, and advising I post my important messages on the web or convert to pdf instead...well they don't really move things forward.
I think there may be a misunderstanding here. The problems you have are mainly caused by the fact that you cannot set the font seen at the other end, whether that is Outlook or any other mail client, using Mail > Preferences. You have to do this by selecting the text and setting the font in the New Message pane for each outgoing individually. Also you may need to choose a font which is different than what you have set in Mail > Preferences. Failing to do things this way results in an email message which contains no font info for the other end to read, so whatever is the local default (TNR for Outlook) is what gets used. Of course many users find having to set the font for each individual outgoing tedious or impractical.
Composing your email as part of your sig does seem to work for some people, but I have seen various reports that it can result messages with mixed fonts and sizes, so I no longer recommend it in general.
Users who want easy control of the fonts seen at the other end are best advised to use another email client, namely Entourage or Thunderbird.
There is no indication so far that Apple is considering changing Mail's behavior. It has worked the same way for 5 years now, and over that time many users have sent feedback asking for a fix. You can add yours here:
http://www.apple.com/feedback/macosx.html