The weight penalty for the plywood is not much, but it cuts into your usable weight. If the laminate is loose then once you remove the countertop you should be able to pull it the rest of the way off. It may require some heat, or being left in the sun for a few hours to get the still stuck glue to release. You can hand sand the old glue off with some 150 grit paper and relaminate the original top.
In my current MH I replaced the countertop and used new wood, but I have a higher useable weight so a few pounds of wood was not a big deal. I did however need to pull the laminate off to recover the edge trim. Oddly enough it was an aluminum band
I guess they wanted to keep the edge thin. The sun did the trick and I was able to get a thin putty knife under the laminate and pop it off. They seemed to use a spray on system for the contact cement and with age it will release. In the case of relamination I would use roll on cement to help fill the roughed up base.