In Naim terminology they tend to rate upgrades in a hierarchy order, which is source first , followed by pre amp and then power amp, as you move up the upgrade path in terms of electronics. But don’t overlook the quality of the speakers that have to do justice to the quality of those electronics. A good balanced set up is always the wisest decision.
So I would say a xps-dr would have the most profound effect and then after that a hicap-dr.
The hicap -dr would then take you onto the logical path if you were to choose to move into the world of pre/power set ups and the 282/hicapdr/ 250 Dr is a significant step up from say the sn3/ hicapdr.
Of course there is nothing wrong with being content with what you have already and just because there is an upgrade path you really don’t have to exploit it.
Those 2010 units are probably not worth it and better to resist the need to scratch that compulsive itch until a more sensible option comes up. Those two units will likely require a service soon and that will cost you from £300 to £500 so always bear that in mind when buying used (recommended service levels 8 to 10 years old).
I’ve been buying Naim used for practically 20 years and have never had a problem, as Naim gear is well made and reliable and looked after in general. There is always an element of risk but you can save a fortune this way, unless you are flush with money. Naim generally has good resale values as the Naim/hifi habit is contagious and Naimies often are on the upgrade path so someone is looking to sell or buy always.
So yes xpsdr first and hicap dr second. But if the hicapdr comes up at a silly price first go for it, if you still have funds for the xpsdr at a later point.
Buying used Naim say two/ three years old should make a significant saving and you won’t have to service them for several years.
Don’t forget a good rack and a dedicated mains set up at some point too, if you want to extract full performance and become a real hifi nerd. And keep well away from this forum, if you want to stop at the two suggestions I made, because you will get sucked in thereafter and start becoming somewhat obsessed, putting power supplies on routers and doing odd things with cables, a bit like me!
Hope that helps with good decision making.