Well back when I had a darkroom I started out with an old Gnome/Wray enlarger, which was given to me by a friend of my dad, when I was about 10 years old or so. I finally ended up with an LPL C7700 and Nikkor EL 50 f/2.8 lens for 35mm work. I did start by adding a filter holder to the Gome, and using the Cokin like square filters for Ilford MG IV papers, and then a two bath dish developed colour process from Agfa for prints from slides. Again I used it with the filter holder and a set of square filters. A friends dad worked at Agfa UK and got me the sample kit, with the filters, that they made. That made me want to move to a full colour darkroom when I had the chance.
I had to get rid of the darkroom kit when I split with the Mrs, and my film cameras were with my slides/negs when my flat got flooded and I lost the lot. Since I had already felt that 6 MP CMOS digital sensors were a specific advantage over film, especially when I needed to end up with digital files. I went with just staying digital, and didn't replace the uninsured film kit.
So now it's Lightroom and Photoshop CC, coupled to a Canon Pixma MG 5150 printer, and the ability to upload my images directly to devices I could never afford to have at home, via the two pro labs that I use. It's a much improved environment too, although I do miss the intangibles of working in a darkroom under safelights, with the smalls of the chemicals etc.
Actually you bring up a good point, in that improvements to image processing software over the years has also helped older bodies remain relevant, certainly if you shoot RAW. If you are only going to shoot in camera JPEGs, then you may find a newer body has more advantages as the improvements to processing are applied to the camera. But that is one of the things that would be covered by specific features that will help you in your photography.
If I had the money to do it then I would quite like to try out shooting with large format film, and working with it in the darkroom. Are you still wet printing at home, or are you using digital output for your film work?
I'd still generally rather improve glass first though.