Putting a new layer of varnish over the drum shell will affect the tone somewhat, depending on how thick of a finish you put on. Unless it is very thick coating (like automotive clear coat or epoxy finish) you are unlikely to notice the difference.
Putting a gloss coat on a matte finish series instrument will affect being able to resell it to someone that is replacing that piece in a kit, or who is looking for the original look of the model.
The series itself doesn't seem to be in the "collectable" market, so you should be able to sell it as an individual drum on the used market for whatever the going rate is for that type, unless you end up with a bed finish job.
Getting a good, clean, gloss coating on the drum will not be a simple job.
You will have to seal the matte wax finish with a sanding sealer, then apply multiple coats of finish, with sanding in between, before doing a final buff and polish job. This can be done by hand with hours and hours of work, but having the right tools for the job would be the best way to assure a good result.
There are many options in the types of finishes available, and different ways of approaching getting the high gloss finish. Each method can have a different process and result in different thicknesses of final finish. You will want to do some research on woodworking and wood finishes to decide what method is best for you. You also might bring this question to the woodworking stack exchange: https://woodworking.stackexchange.com/
Edit: Almost forgot, In some cases the matte finish on music products isn't a true wax finish, but a thicker coating that has the gloss removed. I have found in some cases (guitar and ukulele) that the coating is thick enough to polish out to a gloss finish with no additional coating necessary. I can't tell from pictures of the drum set, but this may be the case and worth looking into.