That's a fun question that's been discussed on Cubase users Facebook groups A LOT! Obviously I have Cubase 10 installed but when it comes to producing and everyday work I still using v9.5. I will tell you why in my opinion you should or you should not upgrade to v10.
If you are still using anything below v9.5 like 8 or 7 then you definitely should upgrade. Steinberg introduced the brand new 64bit summing engine for Cubase since version 9.5. I was blown away by the quality of the sound. What I will say might be questionable but I strongly believe the engine matters. Why many producers and pro studios use Logic or Ableton for creating songs but Pro Tools for final mixing and mastering. The reason is - the quality of the Pro Tools engine. Pro Tools is unquestionably the leader in this territory. However Cubase Pro can easily compete now with its new engine. You will be amazed how much clarity you gain switching from versions 7 or 8 to version 10. If you still on 9.5 and you don't have the need like me to have "the latest things" you might easily stick with what you have.
That is why if you still using 9.5 you might feel right at home. It is all about the workflow. There are not that much changes when it comes to new plugins and features with version 10. It is more about the looks, the workflow, the new gadgetry like the new audio alignment feature (those things I have been doing manually for years). Steinberg has this weird habit that the real changes are in the "half versions" like 8.5 or 9.5. Simply wait what the Steinberg wizards will introduce in the 10.5 version that also will be way more stable than the current one.
You should definitely upgrade if you are using Cubase Artist or Elements. First of all I'm using all the features of the Pro version in my templates. You will not hear the results of my work opening my templates on your striped down versions. Second of all, you really have the full and complete music production power with Cubase Pro. It is the most powerful DAW on the market in my opinion.