The .to TLD is for Tonga, as I'm sure you know. The "actual" use of it, I've found, is more within Toronto - a lot of people think it's made just for that city, just as many think that .tv is just for video websites, when in actuality, it's the TLD for Tuvalu.
"Visa" is a generic word; it refers to a document which grants its legal bearer the right to enter a designated territory for a fixed period of time. Thus, the financial services enterprise by the same name would have a difficult time to pry it from you... but they have the means to outlast you in a legal battle, so consider it possible for them to come after you and tie up your time and money.
Putting that aside, the "highest and best use" for this name is unclear, assuming it can maintain its status as a generic.
I would value this at low $xxx, given the liability to be caught up in a legal proceeding, and limited possible use for the name.
Note that Visa Inc. does own most "obscure" extensions of its name (i.e. visa.mx, visa.io, visa.es, visa.tk, visa.cx, visa.ky, and visa.so, to name a few).
One noteworthy one that they don't own is visa.ch, for Switzerland; which I would think is a very key one for them to own, being such a financial haven!
The website uses the word "Visa" for its generic term, so I would consider it virtually impossible for that name to be pulled away from its current owner.
That, in my opinion, is the best use of such a name for the sake of holding onto it.