I don't think that a new amp will give you the pleasure of buying collector quality source material. An audiophile record is a joyful thing and you get to repeat the experience with each new title you buy.
I have a digital desktop system with a Denon PMA 2000ivr and a pair of Polk bookshelf speakers. I also have a main system with large Thiel speakers and Krell amplification that includes a turntable. My little desktop system sounds amazingly good.
I've got a couple of suggestions that will leave you with plenty of money to buy nice records.
1) Your turntable is excelIent but think a cartridge upgrade along with a separate phono preamp would be the best bang for your buck. I can vouch for the Hana SL cartridge. I have this in my main system and it made a big difference for the better. It has received stellar reviews. Regarding a phono preamp, there are lots of choices and you don't have to spend a lot of money to get a good one (Music Direct has a bunch of them). The key feature to look for is the ability to adjust the impedance for MC cartridges. There are also lots of choices used. Your Denon is a good amp but the phono section is its weak spot.
2) I bought a Black Ice Foz SSX Soundstage Expander for my smaller system and I really like it. You can narrow or expand the soundstage and a separate control adds bass warmth. It made a significant positive difference and costs about $600.