The bike was built for 126 mm rear spacing. If the rear spacing is now 130 mm, it might not be a good idea to return it to 126. As a 130 you can put on any drivetrain 8-speed through 11-speed, as long as the hub is a 130 hub. I agree with Randy, going to 135 is not recommended, and you can get all the gear range you need with 130. If you ride road, the wheel strength will be adequate even with touring loads.

If it was now 126, I'd say go for the 126, but I don't think it's your best move now.

As far as the SunTour, I think it's a good direction, but there are many that you can take.