I'd add at least 3 North East seats (Aberdeen South, Aberdeenshire and Moray), Perth (North Perthshire more than the South), the the other border seat you've missed out and possibly a couple of others in Edinburgh as being in play. The local SNP branch have been pretty vocal about how much they dislike Paul Monaghan in the Highlands, the lib dems will fancy their chances in Fife North East as well... The Tories in Angus.
At least 10, probably more, seats the SNP currently hold in play I'd say. The SNP will be able to rely on a couple of % bump in some places where the greens aren't standing though.
I'd agree as well that some of the left leaning SNP voters may be tempted by labour's offer.
Even if the SNP lose 10 or so seats (which I still think is unlikely) that can't be cast as a failure. They'll still hold 4/5ths of the seats in Scotland and will comfortably win the election.