I'm going to be seeing as much of the Isles as possible before and after the empeg meet. Can anyone suggest when the tourist spots are less full but the summer fun is in full swing? Also, suggestions of what to see would be great.

Off the top of my head, all I can think to see and do are:
Stonehenge
The Adventure Centre rock climbing superstructure in Scottland
One or (preferably) more superstar DJ club nights at the UK's hottest venues
... and a visit to my castle, if it hasn't already been stolen (but that's a LONG story)