Although wrapping the starter will protect it from some of the radiant heat from the headers it will do nothing for the heat-soak from the block. Indeed wrapping the starter may act like a tea cosy & stop the heat escaping.
However my starter is wrapped- more from habit than anything else.
When I started to get starter problems, some 10 years ago, I went through all the various fixes. I worked out that a short path for the battery/solenoid activation wiring, plus a relay, is paramount. Secondly, as Norman has said, check the resistance of all the wiring to the starter & alternator. I have now simplified my wiring & have a spare alternator/starter loom waiting to be fitted as & when.