Actually your mechanic is correct, pipes are going to hurt fuel economy, make it more finiky, and hurt reliability slightly. However the degree of this is left to the owner, if you do them right with the SRX base gasket, opticool, head mod, rear heat exchanger, proper tuning and monitoring with EGTs then they can be reliable. Some vipers have seen more then 5000 miles of performance with no issue. The ones that pop are the are the people that rush them and don't take the time to tune it right and cannot stay off the throttle when freshly installed.
The only draw back I saw to pipes was poor fuel economy (well poor for a yamaha bought like any cat or skidoo, 8-10mpg), and a long pull across a lake the EGT's can just keep climbing and you have to have the retraint to let off. Otherwise they are bar none the best performance mod you can do to the viper.