We put a huge 8kW system in last year (our annual bill was $3500+ as we are big users, mostly our reverse cycle refrigerated aircon is the culprit), we've had 3 bills since (the first one was only a few weeks of solar in the qtr) and are soooooo glad we did! We've already saved well over $2K. One thing to consider is to get provision for more than you might need now, in case you wish to add panels later (eg as your family grow), as otherwise you will lose the feed in tariff if you upgrade and have to apply again and get whatever feed in tariff is going at the time. We have approval for 10kW and will keep our feed in tariff (about 27c) up to 10kW. It costs nothing more to apply for a higher approval. Also, we wanted to be in credit as then we are able to transfer that onto our gas bill. This year our electricity usage has been higher as either myself or DH have been on parental leave since June last year, once DH goes back to work in Sept it will go down as we will be at work during the day so we will save about $4-500 more per year.

* is it over capitalising to get solar panels installed?
Only if you plan to move before the solar panels start paying for themselves
* will it add value to the house? Or can they detract from the value, given how they look?
It would add value, as long as they are properly installed and as unobtrusive as possible, the house across the road from us has two different types of panels, and to be honest its ugly. We have 32 all installed neatly and it actually looks pretty cool
* how long does it usually take for the panels to start paying for themselves?
3-4 years if you are looking to zero your bills. It really depends on what you get, if you get a smaller system but still have some bill to pay then it will take less. We felt that if we were going to invest and outlay all this money then we wanted no bill
* do they need much in the way of maintenance?
Not really, generally the rain gives them a clean, otherwise getting up on the roof every 6-12 months with a broom to get rid of any bird poo might be necessary (we haven't needed to do that). If they get too dirty they aren't as effective in generating electricity, if you have heaps of trees around your roof and lots of birds dropping their mess this would likely be an issue, we live in a new 'burb and there are no trees that high yet
* who on earth is a trustworthy supplier in Melbourne? A quick look at some of the "deals" being offered recently on TV shows some horrible reviews of shonky service and very long lead times to installation, as well as dodgy "upgrades" being sold. I do not understand a lot about electricity terms, so the options can be very confusing.
Have a look at some of the solar forums, we did and found out who NOT to use! I'd recommend the company we used but they are local to SA. Also be very careful with going with those that have a high feed in tarriff. Often this is only for a short period of time, then drops back to quite a low tarriff, and are often more expensive to install, so you probably aren't any better off.