I went the MBP13 route myself, but the wife is a very casual user. The i3 base config will do her fine.From looking at the results I'd say the heatpad is very much 'what's your use case?'
It bumps up the multicore score a bit more than just the shim, but does increase the case temperature (we still don't know by how much).
So if it's at a desk and you want max sustained performance for a 12w chip, the shim and the heat pad would be the way to go.
I'd say if you want a thin, light and still very powerful notebook that's mobile, the shim and repaste will be enough for 90% of users.