If you're not having any problems then there's little gain is "upgrading from a Superhub 2. If you've got a first version Superhub (or older modem) then they should replace that at their cost anyway - there's a very slow moving plan to move everybody onto Hub 3s because it reduces cable network congestion by using more channels. Personally, I wouldn't pay VM a penny for a Hub 3 "upgrade" - their property, their responsibility. If you want better wifi, your best option is to put your existing hub in modem mode and buy a better wifi router. If you're having problems, get VM to take ownership of the problem and sort it out - the hub is their equipment and you shouldn't be paying them extra to replace faulty equipment that is their property.
If you take any problem to tech support, it'll take a long time, and they may not fix it. If you contact customer retentions then they'll often give you a new hub but also offer you a "free" speed upgrade. Sounds good, but be aware that's often a time limited discount to keep the price the same as your current offer - although if you're currently on a legacy speed (like 60, 75, 150 Mbps) then they will move you up to the nearest of the current standards, and your price would change. If you take the "free" speed increase, then you'll have a new one year lock in, and after 12-18 months your discount will expire and you'll be asked to pay whatever is the going rate. I'm not saying don't do that, just be aware how it works.