Again, I'm not advocating inflation. I'm proposing a variable transaction fee to compensate for negative effects of inherent deflation.
All major currencies are far more stable than Bitcoin. Bitcoin prices swing over 10% each and every trading day, when was the last time USD did that?
This would be a hard fork and you would likely get very few people to switch to something that guarantees they will lose a certain amount of value each year. However, you are certainly welcome to fork bitcoin with the changes you propose and then you can see how many people agree that this is what is holding bitcoin back. Instead of trying to convince us here, just grab the code, make the changes (it seems pretty simple to add code to calculate the fee as you propose based on coin age), announce that as of a certain date, FeeCoin will start, using the bitcoin blockchain as of that date (or make an alt and start over). If this is really what will hold bitcoin back in the future, it should be easy to get a critical mass of users of bitcoin to switch to your fork. You'll be the bitcoin savior. If a majority switch, it might even adopt the name Bitcoin 2.0.
The real way to find out if it is a good idea or not is to put it out there for people to use and see what people choose freely. My opinion is that people won't choose to use something where they are guaranteed to lose value. People here won't be able to determine that by talking. ;-)
Anyway, just because someone calls something that acts just like inflation - eating away the value of savings each year - something else doesn't change its nature. You assume several things too: first that bitcoin is and will remain deflationary when it has an expanding monetary base and second that a currency with an eventual stable number of units will be deflationary.
The nature and value of bitcoin do not depend on the exchange value for fiat currencies. If you read more about bitcoin, you will see that it is more than a currency, providing value (like land as someone said above) and that the exchanges are merely an entry point for non-miners. Changing the bitcoin protocol to do something to promote exchange stability is outside of the bitcoin idea since that would inherently cause inflation in bitcoin due to the inflationary nature of all fiat currencies when controlled by a central bank. E.g. if you want to essentially try to peg bitcoin to the Euro or Dollar, you will be importing their inflation and that is a bad idea.
:-)