Non-erasing Turing machines and loss of generality
Your definition of non-erasing Turing machine is "not the common one". Turlough Neary nicely summarizes early definitions and results for non-erasing Turing machines:


  Non-erasing Turing machines are a restriction of Turing machines that are permitted to overwrite blank symbols only. Moore [Moo52] mentions that Shannon had proved that non-erasing Turing machines simulate Turing machines, however this result was never published. Shortly after, Shannon proved 2-symbol Turing machines universal, Wang [Wan57] proved 2-symbol non- erasing Turing machines universal. Later, Minsky [Min61] proved the same result as Wang using a different technique. Minsky proved 2-tape non- writing Turing machines were universal and showed 2-symbol non-erasing Turing machines simulate these non-writing machines.


So here it says "overwrite blank symbols only", while you wrote "cannot replace a symbol with a blank unless the symbol under the read head is a blank".



In general, it seems that being non-erasing is not a serious restriction, but the answer here has one reference with results that point in the opposite direction:


  
  John E. Hopcroft, Jeffrey D. Ullman, "Nonerasing Stack Automata". JCSS, 1(2):166–186, 1967.