If I buy a new MacBook Air 2020 (i5-512gb), how long (years) can I use it or should I wait for the new MacBook Pro 2020?

How about:

If I buy a new Mini, how long can I use it, or should I wait to buy a new transit van?

or perhaps:

If I buy a new single oven, how long can I cook with it, or should I wait to buy a new double oven?

How would you answer those questions?

Here’s a 3 step process I use for choosing:

Step 1:

• Am I being held back by what I have currently?
  • No
    • Continue using what I have
    • Go to End
  • Yes
    • Make a record of how I am being held back
    • Proceed to Step 2.

Step 2:

• Is a suitable replacement available now that will address the ways I am being held back (refer to notes from Step 1)
  • Yes
    • Buy replacement
    • Go to End
  • No
    • Make a record of any issues a replacement doesn't address
    • Go to Step 3

Step 3:

• Can I adapt around what is holding me back
  • Yes
    • Adapt
    • Return to Step 1
  • No
    • Sulk for a while
    • Return to Step 1

End:

• Congratulations! You made a decision.

In the specific case of a MacBook Air here's what happened with my 2010 MacBook Air

• 2010 - Purchased
  • 2010 - 2014 - Perfect choice
• 2014 - Needed additional power sometimes, for software development
  • Purchased most powerful MacBook Pro available
  • Used macBook Pro at base
  • Continued to use MacBook Air for travelling - still worked great, just a bit slower for some things.
• 2016 - Spilled red wine on MacBook Pro, Oops.
  • Used MacBook Air as backup while deciding whether to repair or replace the Pro. Air still worked great for most things, just a bit slower for more demanding work.
  • Bought replacement for the Pro
• 2018 - Took a break from travelling
  • Used MacBook Air as media player.
  • Drowned MacBook Pro sprang back to life. But screen has a 15% vertical strip at the right edge that is not working and thunderbolt ports not working.
  • Started using resurrected MBP as a development server and media processor/streamer.
• 2019
  • MacBook Air not getting used much.
  • Sold Air to someone who now uses it as a media player for his kids, but, to his surprise, has also found he can still use it for many other tasks such as Keynote, Pages, Numbers and non-demanding photo editing.