Join Date: Jul 2005
Location: London, ARN, HEL, ..... or MAN
Programs: BA GGL / GFL, Mucci Diamond!, HH Diamond, Radisson Premium, IHG Gold, Hertz Gold
Posts: 5,926
Basically, back to the OP's original question, being OW Emerald doesn't in itself open up more likelihoods of a cheap upgrade if the plane isn't full.
If the plane is full, then it might improve the chances of an involuntary (free) upgrade which would usually happen in the last few hours before the flight leaves.
So the options if the WT+ cabin isn't full are: to pay to change your existing class at the current going rate, check for AUPs on the App on on the website (cheap upgrades) or use Avios or AA miles (if possible). These are the same options that would be available to all passengers in WT+ unless they have a super-discounted group fare.