http://mpva.com.au/
is one site to look at for Mornington.
Both areas grow pinot and Yarra valley has won many prizes over the years for them.I have visited both areas and have never done a tour of a winery.
IMO the Morningtom area has the restaurants eg Ten by tractor. Yarra has less but still you could go to the Healesville hotel which has great award winning kitchen or De Bortolis.
I love the wineries of Yarra Valley best.
Opening hours would be on the websites

http://www.wineyarravalley.com/
is a site for Yarra Valley

Thanks for the insight and recommendations. We might be leaning toward Yarra at this point, but still a bit up in the air.

Any favorite wines?

The Yarra Valley has plenty of places for lunch. In additon to De Bortoli, try TarraWarra, Yering Station, Tokar Estate, Domaine Chandon, Balgownie, Rochford or several others.

I must admit that when we go, either because we just want a day out or because we have visitors, we tend to stick to the same places. Start the day with a coffee and cheese plate at the Yarra Valley Dairy, move on to Domaine Chandon and do the self-guided tour (remembering that there really isn't very much to actually *see* in a winery, at least for most of the year) and then try a tasting flight ($) of their sparkling wines. Visit the art museum at TarraWarra. Have lunch there or at Yering Station or De Bortoli or Tokar Estate. If time and interests permit, consider visiting the Healesville Sanctuary while you're there.

2011 national wine show gave the best pinot noir to Lasatia Park -a wine devloped by De Bortoli and Shelmerdine.
One of my fav places was destroyed in the bush fires a few years ago.

Most wineries don't genberally have tours as such, but will show you around if you are really interested. The vast majority don't charge for tastings either.
The bigger ones will be open every day and have acafe etc.
The Medium ones will be open most days and probaly not have a cafe but will possibly do you a coffee.
Smaller ones may only be open on Weekends and/or by appointment.

If you choose the Mornington Peninsula. They have a brochure that shows all the wineries colour coded by when they are open.I expect the Yarra Valley will have a similar brochure.

I haven't been to the Yarra Valley for a long time so can't comment. We spent a week on the Mornington Peninsula last January and loved it. Apart from the Wineries there are two breweries; a fantastic (literally world class)chocolate shop at Flinders, wonderful icecream at Sorrento (Mubbles), some great fish and chips in Sorrento as well (The Baths Also a restaurant)and fruit & berry farms and a honey farm.

Then there is the Hot Springs near Rosebud for a realaxing time after the wineries (witha children free zone for us without kids).

There is also the bay and ocean beaches with cruises. Snorkelling under the Balirgowrie Pier is magical. Plus there is the Historic forts and Quarantine station on Point Nepean.

No idea about the wines though, but there are some 100or so wineries.

Yarra Valley is forests, wines and yuppies.

you forgot the yuppies in Mornington peterSale!! Probably no more forests in Yarra than Mornington eg around Red Hill

No I didn't, they are balanced by the Bogans on the Rosebud Foreshore.