Worthy or not depends on you can put it to use.  For instant, if your current memory usage is less than 50% being utilized, adding another 32 GB of RAM and let it sits unused will not be a good upgrade.

However, the T5810 is still a viable machine, upgrading to NVMe drive is worthy and you will actually see increase in performance, apps loading, files transferring, etc.., a simple PCIe to NVMe adapter can be installed on slot 1 (closest to CPU) and it will allow to use as boot drive as well.  Adapter with heatsink is suggested.

Additionally, for less than $8 usd, you can upgrade the CPU to a 12 cores E5-2680 v3.if you have the needs for CPU cores.

Certainly the memory upgrade plan is worthy as well.  Check your current RAM specs and getting the same type for compatibility.  They can be had at very cheap price from surplus supply sellers.  Due to the system age, give it a fresh new CR2032 coin cell battery while working on the motherboard.

Refer to user manual and take proper precaution.  If data is important to you, make certain that you have them backup externally.

You are all set.

Your nVidia card should be installed on either slot 2 or slot 4 as they are PCIe x16, with 75w slot power.

Glad to hear that everything went well for you. 

It's good to see you reporting back with the upgrade result.  Everything looks great.  You may consider to mark as resolved by select any helpful post and Mark as Accepted Answer.  It will help others with the same upgrade inquiry.