Mac26Mpaul:
Being a glutton for punishment, I've done both.
In 2008, I got a local trailer manufacturer to upgrade the capacity of the original Mac (steel) trailer to 2.8 tonne (see my optimistic report
here).. At the time a new trailer matching the load capacity specifications was likely to cost around $15k so the original quote of $6k seemed like a good way to go. However, it ended up costing around $9k by the time it crossed the compliance-plate finishing line.
The upgrade turned out to be an expensive disaster. Although the trailer towed okay and survived a couple of long distance trips (including Perth-Shark Bay), launching and retrieval was horrible, it gave the boat a very hard and bouncy ride and I had ongoing problems with the winch, mudguards, lights, and finally failure of the beefed up suspension.
In 2010 I gave up on the upgraded steel trailer and bought a new aluminium tandem axle trailer with an Aussie compliance plate rating of 3.2 tonnes. It has alloy rims, 4 wheel disk brakes, electric over hydraulic actuator, spare wheel, longitudinal bunks, and an excellent winch. The trailer was designed and manufactured in the US by Venture Trailers, but assembled by their local WA agent. Thanks to the strong AU$ it cost a little less than $9k.
It tows very well, giving the boat a much softer, smoother ride and launching and retrieval is easy. I used this trailer for my recent 8,000 km Perth Lake Argyle trip and was happy with its performance overall. However, it has not been without problems: lot-lock, excessive tyre wear and light brackets sheared off.
Hope this helps. PM me if you want to know more.