Neon tubes are commonly used nowadays for setting a specific color temprature of lighting for specialty displays. They can Absolutely be dimmed (And most even require it) as you need to mix the 2 colors of neon to acheive the output you desire to properly light you artwork.

50watt LV may still be 50w, but you really need to pay atention tot he wattage rating of the Transformer. Especially with Track type Fixtures. just bcause there are 3 50watt Fixtures onthat Track the day you set the system up doesnt mean some lighting person (Or even the homeowner) wont throw another fixture (or 5) on that track sometime inteh future. (Its happened to me)