If you like the Spider, you'll like the L35 Ghost Spider. There's no real adjustment to be made, because the meter is the same speed. I like having the additional 15 foot mode. And it is a bit more precise, both on paper and in use, imo. It's subtle though. Don't expect a dramatic improvement. If you're lipping or just missing, more of those might drop.
But if you're 3 putting a lot, it's probably more a problem of technique and/or execution. If you're stopping 3 feet short, rolling 6 feet by, or 4 wide, no putter will cure that. And of course, if your approach shot lands 50 feet away, that's not going to help your putting, either.
You won't hate it, but you might not love it, either. I liked the Spider, I like the L35 Ghost Spider, and I'm glad I upgraded. But if you don't like the Spider, you probably won't like the L35 G.S. any better.
Do the free rental and see.