jhaelen said:

I considered it early one, but decided not to do it for a number of reasons:

Working from memory here, so feel free to check me out: Actually some of the expansions do this subtlely already.  CotDP with 18 cards adds 1 gate to each location and two to the major gates.  So increases chances of a  minor gate (From 3% to 4%) per gate location.  OTOH, KIY only adds to the 7 major gates and so decreases the changes of the 4 minor gates.  DH adds 1 gate burst to each of the medium gates and 2 gate bursts to each of the major gates.  Mixing all expansions probably brings it back to a more predictable distribution.

If each gate is equal, then this would indeed make a more frantic game.  Sealing six gates would be less effective as the chance of a gate bump would be about half (9% per gate) of what is was before (about 16%).  So I'd say it might add three gates to a normal game.  Can you handle three more gates?  And it would, as you point out, reduce the number of surges and monsters to deal with.  Personally, I think there are too few monsters now.  Of course, you could fix this by having more monsters come out with each gate and/or surge. 

Gate Bursts would become less effective, since there are none for the minor gates, so they'd be the tactical choices for sealing.

Kate would be less effective since she'd be less likely to stop a gate from coming (though her encounter chances would be the same).

Other subtle or unintended changes:  The Science building would more likely have a gate so less trading in for clue tokens.  I think the historical society and science building have a few more clues than normal (not sure here) and so there'd be less clues on the board for them.  Would you keep the clue distribution the same?

The major and medium gate locations are also more dangerous to have encounters in. Since they'd be open more often than before and might have clues on them, investigators would be having more dangerous encounters.

Now if you really want to have a frantic time, let every LOCATION have a chance for a gate?   Including Kingsport!!!