Leaky valves ?? What exactly does he mean? Valves can leak in two ways. Either valve stem seals are leaking oil, causing high oil consumption and posible oil fouled spark plugs, or they are burned and the engine wont hold compression. Since you mentioned that you had to replace the spark plugs, I assume that oil fouling and the valve stem seals are the culprits. If the engine compression is good replace the valve stem seals and the timing chain, rails etc. That will be alot less expensive than a removing the heads and doing a valve job. These engine usually dont need a valve job at 89k miles, but they do need seals.
The price quoted for the engine mounts sounds really very high to me. You might get a second opinion from a different more trusted shop.
I got too many cars!! Insurance eats me alive. Dave
78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k