I had thought that my rather ‘homemade’ RPi set up, might be inferior to an expensive off the shelf streamer. I take it from what you say that that ‘ain’t necessarily so!?
It doesn't require much money to get audibly neutral digital (assuming that is what you are seeking) but some of the cheap stuff fails for cost cutting reasons and some of the expensive boutique stuff fails but for other reasons. Much of the Raspberry Pi hardware is designed and built down to a price and by semi-hobbyists rather than experienced engineers (e.g. kickstarter projects and similar). This tends to show up in the quality of the design and possibly manufacture making it unwise to assume competent technical performance equivalent to that from hardware bought from the larger reputable pro audio companies. The performance of your current hardware may or may not be fine but since there is no longer any reliable way to look it up given the state of home audio press and forums such as this you will probably have to faff about working it out for yourself by measurement and/or listening tests against a reliable bit of pro audio hardware.
Cartridges, tonearms and to a lesser extent turntables are not audibly neutral and so wisely spent money will be reflected in a more audibly neutral sound (assuming this is what you are seeking). Unfortunately the home audio press and most forums can be very misleading about what is important to technical performance, what is not and, in some cases, what is detrimental. Your current setup looks to have reasonable performance but at an inflated price because of the strength of the brands in the eyes of some audiophiles.
In your position I would look to sell the turntable and replace it with a cheaper one with roughly the same performance using hardware from brands with less "audiophile appeal" but around the same technical performance. Even if you intend to mainly listen to digital sources it makes little sense not to have a turntable if you have a record collection. Like most I switched over to the improved sound quality and convenience of digital as the main source 30-40 years ago but I still have a record player which I use now and then for the odd record that I have not yet digitised or if borrowing a record. I haven't played any of my cassettes in over 20 years and suspect they may be unusable, DAT and reel-to-reel are long gone and not missed but records are still around.
Unless interested in the Raspberry Pi as a project I would look to replace it with decent mainstream pro hardware. It is likely to be a hundred pounds or so more expensive but reliability and build quality will almost certainly be improved and sound quality might be. It won't get worse (in the audibly neutral sense).