The new silicone is good. I have heard from lots of people that they had the same glass tank for 15 years. I had a tank from the late 60's (Inherited) and the tank was leak free. I broke it in the 90's so it was around 30 years old.
I have heard acrylic will yellow over time. Plus i havent seen a acrylic over 10 years to compare it to the glass. Probably because they haven't made it that long. Too much hastle and money in my opinion. I wouldn't trade my glass tanks.