Another vote for leaving the Lull alone. Even if you do a spectacular job at defretting, it will reduce the overall value, probably by a fair amount, unless, maybe, if it was done by Lull, but that would be a spendy penny, too, I would think?
The idea of getting a good-quality Fender or G&L makes sense to me. Look for a fretless. If a fretted comes along that is also super cheap, you can go for that and defret it. In the meantime, enjoy that Lull!
The one bass that's interesting to me, and is affordable is the G&L Kiloton. That is definitely an option. I'm keeping an eye out for one.