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I've uploaded every proper ride (I don't Strava commutes) since I bought my 800 in December 2011 and I have to admit I've never thought "that's inconvenient" but I can see it's more convenient.
I'd just check how stable/reliable the 820 is. Garmin have a habit of releasing products that are frustratingly unstable/buggy and I'm reluctant to upgrade my 800 because it's very stable and reliable.
Trust me when I say that your Garmin freezing or otherwise crapping out on you when you're relying on it to get you round a long ride is not convenient!
I think @hippy feels the same way ;)
It's not effort, it is the inconvenience.
I intended to do this when I got the 800, and did it a handful of times and generally just do not bother.
Upgrading is about convenience not about effort. If it's one more thing I don't have to remember to do, one more time I don't need to put the computer on, remove the SD card or GPS from the bike... then great. I'm far more likely to use it.
The 800 gets a few outings a year for solo rides where I need routing, an 820 that constantly syncs via the phone would be used on every ride.
The value I get from the 800 because of the inconvenience is low. The value I'd get from the 820 would be high if the sync'ing just means I'd leave it on the bike all the time and only charge it every few days.