Don't worry about the gauge problems, they are common with all boats using Keyser Medallion (borg warner) gauges. Malibu, MC, Supra use or have used KM gauges. Tell your dealer to clean the connectors on the MMDC gauge computer box. That will probably get rid of the gauge readings dropping out entirely, but an occasional flakey gauge is just normal with this instrumentation package. Nothing to worry about. The engine has it's own computer, no problems there.
Toyota quit making boats because they were very expensive to build (63K) and they had trouble dealing with boat dealers and alienated key dealers. The boats have their issues, like any brand, but they are minor compared with what you gain owning a Toyota.
Seriously, if you pass on this boat, let us know because someone here will probably buy it.