Trying to think of what I need to buy, but I think I've got everything. Most Wii U games that I didn't purchase on the Wii U have gotten ported to the Switch by now. For the Virtual Console I was interested in the Mega Man Zero games but Capcom got those on Switch with the Zero Collection. I was also thinking about getting the GBA Castlevania's but then Konami went and saved me the trouble by releasing them on the Switch with the most recent collection as well. I've been wanting to get Mega Man Battle Network 2 and 3, but I figure it's only a matter of time before Capcom releases a collection of those in the coming years so no real need to get those either.
Even though it sucks when these services shut down, I don't see much that will be lost forever. Most of the NES and SNES games have already been released on the Switch online, or released in other Collections by their third party. The N64 selection on the Switch is going to end up being larger then its Wii U counterpart, and it's only a matter of time before GBA games hit the system as well.
The DS Virtual Console is the only one I worry about since the Wii U was perfect for allowing easy emulation of its titles. Of course, I wouldn't be surprised if Nintendo creates an touchscreen controller add-on to emulate the DS and even 3DS bottom touchscreen so they can add those system to the Switch or its successor someday as well. With how popular the DS was, I doubt Nintendo wont find a way to take advantage of nostalgia for that system someday.