For the original issue, not having a seat assigned in economy does increase slightly your chances of getting an "upgrade", but only as far as E+. However far more likely is that once you hit the check-in window a number of Silvers who currently have seats in E- will move up to E+, freeing seats in E-.
If both E- and E+ are full and an op-up is required, the odds of it being someone without status are all but zero - they are going to move someone with status up, and then give you their seat.
Originally Posted by
diburning
How will he receive his miles though? EI gives 50% RDM and 0% PQM. Would they give him original routing credit in this case?
Yes, but it won't happen automatically - he'll need to call.