MyEtherWallet.com has an "Advanced / Offline Transaction" tab which allows specifying a higher gas limit when making payment transactions to contracts, which is sufficient for most of the basic investment game contracts.  The page is confusing the first time through, but once you understand the steps it's pretty straight forward.  It would work for participating in the majority of gamified contracts being played on this forum.

Mist/Geth still seems to be the best interface for interacting with contract functions.

I expect that Shapeshift's temporary issues are a part of the reduced activity the last few days.  That and people have lives during the week - or so I hear.  There are a few exchanges that have announced they'll be bringing ETH trading online within the next few weeks - I expect a flood of newcomers with each exchange that brings ETH online.