From a practical standpoint, if you're happy with your Wee, it'd be easier to add luggage to a bike you've already set up for yourself.
The biggest, and most common, issue with the Vee has already been mentioned - magnets shifting. The fix is easy however.
With respect to gas gauge, the electric pump has been known to cause issue on some bikes. This is due to the integral filter that over time becomes clogged necessitating replacing with a new unit, or bypassing the stock filter and installing an aftermarket filter in the gas line external to the tank (Wee might (probably?) have the same set-up, so this might be something to deal with regardless). I've got over a 100K on mine, and haven't had an issue so I think it's more an issue of getting clean gas.
Since you're posting in the Vee forum though, I'd be remiss if I didn't say buy it; it's a great bike.
False motivation is better than no motivation.