I'd say you've been unlucky, or the problem only appears close up to very strong point light sources. I specialize in night photography, and have done since the early 1980s. I always use UV/Skylights, and can't say I've noticed any flare problems as a result:
www.nightfolio.co.uk
Here in the UK a big problem on long/night exposures is dew forming on the front of the lens. If I use a filter and it fogs up, I simply replace it with a new (warmer) filter from my pocket, and can continue shooting.
As for easily replacing lens front elements I am sceptical. The only time I had a major lens maker disassemble my lens they tried twice to put it back together properly and produce sharp images, and failed. I am very wary about the ability of even authorized lens repairers to do major work to factory standards - perhaps I am just paranoid.
Your seeing reflection of light off of the highly reflective sensor projected onto the flat filter. A well know problem for shooting with a filter on at night with light sources (even for film).
