I installed 1.09e from an Impulse archive an got to update with 8 MB or so rather than 1.99 GB.
I think there is a different whether you use the Pre-release option on the opening screen or in the general preferences.
Stardock, would you be able to check up on this, and properly integrate both options - so that the pre-release option in the opening screen is functionally *exactly* the same as changing the slightly differently worded "Show Pre-Release (Alpha/Beta) Versions in the General Preferences? I think there is currently a mis-match and things are not getting changed everywhere necessary.
It would be great if you fix this! It would help all your future Impulse games too, I think. 
8 MB is certainly better than 1.99 GB (and I think a lot of people got caught because they used the first pre-release option to update betas etc. rather than the one in the Preferences - General menu).
Best regards,
Steven.
PS: What folders were meant to be automatically cleared with the update to 1.10?
EDIT: Actually, I think the automatic clearing happens with the first load of 1.10.