I've had the same email address since the early 90's. It's a forwarding service as opposed to having my own domain which I didn't have the presence of mind to think of setting up way back then. At any rate to switch email service providers (ESP) I just change a forwarding address with my forwarding service. Result is it's trivial to switch ESP's and no one ever knows my primary (ESP) email address.
Of course using the same email address for so many years has been picked up by spammers over all that time. But I have my own ways of fighting it to a point were now I don't get any spam. In fact I got a little suspicious just this week and disabled the spam discard cutoff. That's how I happened to be back in Spam Protection and noticed during one of the updates my "Add score as {SPAM XX.X}" option disappeared.
Still waiting for FM to put it back (I hope) by reopening the ticket I created the first time this happened last January.
At any rate everybody's universe of spam is different (for the most part) so techniques are different. But writing in Sieve gives me a power I never had before to fight it.
As for aliases, I haven't decided what path I want to take. Create an alias for each new registration? Use a single alias with various names? Still thinking about it. I got all these degrees of freedom at my disposal.
Right now I'm don't need to register for any new things so there is no rush. I've only had FM for a year. I haven't changed the email addresses I have with various sites before moving to FM. They all used an "anonymous" gmail account (as anonymous as I can make it with gmail) which I now have set up in FM as a Mail Fetch account and filter accordingly in my Sieve script. Eventually I will change the registration email addresses of those accounts when I decide what technique I want to adopt.