Well as the course is 37 3/4 miles long, nobody can claim to have spectated everywhere.
There is always a trade off. It depends what facilities if any you are wanting. Most of the course it is just surrounded by countryside. There are still a few places you can get a beer and a burger.
Manx GP is considerably quieter than the TT....More of a club event atmosphere. You generally get the more mature types and those who like the classics too.
There is less put on in the way of entertainment than at TT time. If you like a quiet pint, a rally atmosphere, and beautiful rural countryside you won't be disappointed. There is a lot of history here all around you too.
The capital Douglas is where most of the activity will be, but there are other less busy places you could stay...Castletown, or Port Erin in the South...Peel in the West, and Ramsey in the North.
Give me a shout nearer the time, and I could give more detail for you.
In the meantime, this URL may be of interest:
http://www.iommgp.com/
Nige.