I am gold on BA and KLM and use both lounges at NCL (although most of my KLM flights are out of MME).
THe BA lounge is great, OK it is not as nice as some of the other BA outstations like GLA but there is plenty of space and if you are waiting on the inbound flight to come in, you can see when it has arrived at the gate. The lounge has a well stocked help yourself bar and some nice snacks although the lack of any hot food for breakfast is a slight letdown.
However, the Aspire lounge is not a great experience. I normally only nip in for 15 minutes but sometimes there is an issue finding a seat during the mid/late morning as many places are reserved for the EK flight. Clearly having a manned bar goes some way to restrict some paid guests from getting the maximum value for money but it doesn't stop some trying. I have been refused entry in the past on the grounds that the Aspire lounge was full and was told that I should have paid to pre-book in order to guarantee entry - I do 120 flights a year so that it not happening as I only want a quick drink and some space to check a few emails.
Is the Aspire plus lounge ever busy? Every time I walk past when arriving at NCL or walking to the BA lounge there is hardly anyone in.