I didn't find the song particularly sad. The lyrics were somewhat upbeat by my interpretation, but yeah I guess the melody is a little deceiving in that regard.
Anyway, I like what you are doing here. I have a question though. You joke about Gilmour adding some leads... do you not play guitar leads? If not, why might I ask? It seems like most people start out playing chords and never quite get a comfort level with leads. Maybe I just did everything backwards, because I started out playing blues scales and now all I can do well is pick through scales. I've been playing off and on for 10 or 12 years and I still can't put together any decent chord progressions on my own, but I can lay down some pretty mean licks.