Lots of local backyard body shop guys I used to mix paint for liked using a semi gloss black on their hot rods or customers..
They would come to the store and want a semi-gloss paint,but most everything we had was either a gloss or metallic paint..then I learned they also had a "flattening agent" available in a gallon mixing color--we ordered a case of that stuff and experimented with it and came up with some good results,and some putrid looking colors..
After we got a semi-gloss black a customer liked made up,and one guy painted a 50 Merc with it,like the one Stallone drove,suddenly a lot of people wanted a flat or semi gloss color..we started adding blues,metallic silver,some of the cars really stood out..but some colors came out awful and got shoved aside to be sold cheap later to someone wanting to paint a loader or something..
As for the over spray,tread lightly..
Laquer thinner will take off rustoleum rattle can spray paint, but its kind of overkill,a solvent for the enamel that you want to remove may be less harsh and not flatten the semi gloss or worse,make it bubble up,laquer thinner will eat some enamels..it'll kill gloss on acrylic or alkyd enamels if removed quickly enough,left on too long it may cause bubbling..
I believe rustoleum says to use Naptha for a thinner if your spraying their quart cans and the paint is likely the same for rattle cans,but already has the naptha in it..
I'd try that first on a fairly course towel like terry cloth,though it may take longer and a bit more effort using Naptha ,it will reduce the chance of affecting the semi gloss base coat under the over spray..
Rubbing or polishing compound will likely take the over spray off,but it'll shine up the semi-gloss at the same time..it'll look blotchy..
The semi-gloss paints tend to look "powdered"when you try buffing off the top layer,I think its the flattening compound they put in to make the semi gloss,its like cornstarch or talcum powder..so after the over spray is off you may have to buff it slightly to get rid of that,and it may tend to come back later on..
My paint & body shop experience only comes from what I saw at the customers shops and what they told me---it dates back to the early 90's and beyond,so some of my info may no longer be accurate today--they were going to water based paints when I got out of it ,that changed a lot of things..