Thicker is not always better. If it is a rough base (cement or sand and cement), 28 0r 30 is better. If it is poolcrete or vermiculite base, 20 is better.
No. Replace the liner.
We used Garrett Vinyl Pools they have been around for years.
what you can do in this situation depends on what is under the vinyl liner now.
Inground vinyl is better, their is less exposed part to the oxigene, therefore, last longer.
There is special adhesive for this,sold in pool maintenance stores.
Thick vinyl pond liner.
As long as the vinyl liner pool is inground, it can be converted. But you'll probably have to remove all of the vinyl pool elements until you have reduced the pool to a big hole in the ground and then start from there. All it takes is time and money!
The walls of some above ground and some inground vinyl liner pool kits are made of aluminum.
Some pool companys are not in business. most all inground pools have the same size treads..
If you have water behind your vinyl in ground pool liner, you should first lower the water in the pool to normal levels if it is over-filled. Make sure that the vacuum pipe is clear, unclog it if it is not. Once it is unblocked let the water from behind the liner flow out.
Installers use vinyl liners to create inground pools without pouring concrete. Here's an overview of the topic http://www.poolandspa.com/page232.htm.