Unfortunately, there is no perfect way to pack and do things on tours, at least not for everyone, probably even for anyone - we all have to compromise to an extent, which is again different for pretty much everyone.

I do have a large Ortlieb handlebar bag (the 8 liter one, the biggest one they have I believe), but its contents are more or less always the same, every day of every tour (with very minor differences) - documents and money, phones and chargers, sunscreen and a pack of tissues etc. - it's the stuff I use often and take with me when I leave the bike locked (very rare occurrence, but it happens). The rear left pannier is where I keep everything I might need during the ride (minus food, kitchen and, God forbid, bike parts and special tools) and doubt there has been a touring day when that pannier wasn't opened at least once. For me, it's the most logical place to hold things I might need - it's right there when I get off the bike.

I came back from a tour a month ago and a couple of days before its end I was caught in a very heavy rain, a downpour with large hail, on top of a mountain with no trees to hide. I had to stop on the side of the road and there was no way to avoid the rain getting inside whatever pannier or bag I opened (rear left). Had my panniers not been waterproof, ughhh.... it would have been bad, very bad, regardless of plastic bags and dry sacks inside. Now, I know some people who pack assuming nothing out of the ordinary will happen, and they are often right, but I am closer to the other side of the spectrum.
To make things short (at the end of a long post haha) - I don't know anyone that goes on tours longer than two days who doesn't have waterproof panniers - the risk is just not worth it.

Edit (@ Tourist in MSN). I like your bikes.