Larry,
I decided, though, to try to stick with it today to see how it is going. It hasn't crashed again yet, and my mails are all synced. I made sure to add one account back in at a time, waited for all the messages to download and then added the next account.
I ran into a few problems which I needed to work around. For example, every time you add a new account, if you have iCloud mail enabled the default send address for all the accounts turns into your iCloud address! The solution (which I got from Apple support) is to disable and then re-enable iCloud, which then restores the proper default address for each account. Strange I know. Apple Support said it was a known problem and doing this "kicks it."
Then I ran into that problem where all sent email also ended up with multiple copies in the Trash. That is solved (for now) by unchecking the "save drafts on server" option for each account.
You also have to double-check the smtp server settings for each Gmail account to make sure password authentication is properly set because that doesn't seem to happen automatically.
There is also a buglet where if you change the name of the smtp server it also changes the name of the account description to match - so both have to be the same.
Anyway, I'm still playing with it today. Worst case is that I now have an offline backup of all my emails and I can switch back to Mailplane tomorrow if something goes wonky again.
Like you, if Mail.app worked well there are various reasons I would like to use it. I'm keeping my fingers crossed.
doug