I think 3.5m is a fairly steep price for a soon to be 33yo this late in the season. That's the price people pay for players they can build around, not for a playoff rental.
Also the people who might be interested in him for a top level playoff run despite the price tag will probably reason the same way you do: 2 GS levels knocked off in the week the playoffs start is not ideal even if by miracle his GS improves to 9 next friday. Couple that with a few weeks of high minutes and some GS training, which makes it very difficult to predict whether GS can actually bounce back for the second week of the playoffs, and it becomes a problem.
It will be a hard sell at 3.5m, I think.