I would not really recommend the 'Holiday Buggy' unless there is some sentimental reason for wanting that specific car. Sure, there are a variety of upgrades available for the DT-02 chassic based vehicles, including bearings/suspension/electronics/alloy steering blocks/etc - but even if you spent a ton of money over the long run to purchase every possible upgrade, the end result would be a very expensive car that couldn't compete with much cheaper alternatives.
What is your actual budget? If we had the number, we could offer up more productive suggestions about how to spend it.
I think you could find a better base to start with in roughly the same price range.