I think I needed to preface the "remove it from the mount" statement with a bit more info. I would say I have removed less than 1% of my slides from the mounts to scan them. Those were the best of the best images. (EDIT,EDIT,EDIT.......) The rest were scanned in the mounts. Carefully focused and cropped and scanned with the exposure set for each slide. It's not hard to do, and with practice, probably takes little more time than sorting through slides and then batch scanning.
I too started with a Nikon LS-2000 and moved on to the 9000 so I could scan my 6x7 and 35mm film with one scanner. The Epson came when my previous flatbed died.
Your mention of your Plustek not handling dense/dark slides well is why I said I doubted the specifications on the Plustek and Pacific Image scanners. The Dmax is the most important number a scanner can have and the one most often "inflated" by the manufacturers. As I recall Nikon advertised a Dmax of 3.6 for the LS-2000. Plustek says it's film scanners are also 3.6. Unless technology has allowed a much cheaper but equally performing scanner to be built, the price point of the later scanners simply doesn't match what they claim. IOW you get what you pay for. That said and me having no hands on with the Plustek scanners, I would imagine that for most images the Plustek would do a good job and produce a decent scan. It's when you get to the deep shadows that a scanner is really challenged. The problem is if you shot Kodachrome like most of us, you have a lot of dense slides.
One thumbs up for the Plustek scanners is they come with a version of Silverfast software. Silverfast is more or less the gold standard in scanning software, and depending on how well featured the version distributed with the Plusteks is, a very good program. Vuescan has been mentioned and is also an excellent choice. I would strongly recommend the pro version. I have it and use it frequently. The producer of Vuescan is constantly updating the program and it will work with virtually any scanner.