The answer depends on so many other things. MTH has made some great solid running models over the years that are worthy of upgrading to the latest sound packages. Has it just sat on a shelf or in it's box? Has it been run for huge amounts at a time at shows?
The less you pay for the engine, the easier it is to justify the upgrade. There comes a point where you should just buy a new one. Sometimes there isn't any others to buy so I upgrade.
