Civic EG

Would it be stupid to use washers on the top hat studs between the body and top hat to get a little higher?

just curious, why are you chasing to raise the rear?

and as for your query, its not the safest option adding washers to get the extra height as the strut top needs to sit flush to its mounting point for rigidity.

if u wanted to take a similar and safer approach to what you had planned is make a "spacer plate" that has the same template of the strut top out of 2-3mm aluminium plate (easier to work with a jigsaw n drill) any thicker uyou would probably want it fabricated for you, n just make multiple plates up till you get the desired spacing provided you have enough thread to bolt the struts down.

hope that makes sense and is of some use for ya