The Price will probably depend on where you are located. Here the upgrade is € 224,50.
If you mean the crossgrade, then certainly, if you own the necessary competitor software to qualify for the crossgrade.
You can upgrade, but you can not run Pro 10 without the USB eLicenser.
If you record an instrument (vocals) in a room and then compress it it’s often the case that the “reverb” gets more apparent.
Compression reduces peaks. Generally people then adjust the total level after compression by using “makeup gain”. So the effect is that the loudest parts are as loud as before, but the softer parts become louder.
These softer parts can absolutely be the sound of the room that the instrument was recorded in, so in other words compression can bring out the natural “reverb” of the room.
I this is not the problem then you have to show the project with any plugins etc so we can help you troubleshoot it.
I don’t think this has anything to do with latency.