Just read Jay Ham's article on thinning silnylon, and have a few observations.
Discussions with the technical folks at Duco (the glue and sealant people) produced the following information:
1. Thinning silicone resin with mineral spirits or anything else weakens the cured resin because the slurry structure interferes with the resin forming long polimer strings as it cures.
2. If you want thinner silicone sealant, buy a thinner silicone sealant. It will be a unitary formulation containing no thinners, just a thinner formula of resin.
"Permatex Flowable 100% Silicone Windshield Sealant", available at any auto parts store, is such a thin, unitary resin.
I have used Permatex for both sealing and glueing seams for over a year and just finished 6 months on the AT with all my silnylon seams sealed with it. Compared to Silnet, it is tougher, less sticky, more liquid with better penetration, and perhaps more UV resistant. It cures to the touch in 30 minutes, sets as a glue in 20 minutes, fully cures in 24 hours. It's also cheap - half the cost of Silnet for twice the amount of product.