I'm in a similar boat to the OP - my employer is tightening up on personal usage of their work-issued Macbooks, so I'm having to migrate my personal stuff off their M1 MB Pro from next week.
My 2012 iMac has been in the loft since I moved house a year ago - my secondary device is a 2018 iPad Pro 11" - so I'm set on replacing that as my personal machine with a Mini to use my existing nice LG 5K monitor & Magic Keyboard / Mouse.
M3 won't be needed, but I'd be disappointed to buy 'the old one' potentially weeks before 'the new one' drops, especially as I'll be keeping it a good while.
I just went for it now - M2 / 256 / 16 coming on 5th September using Education Discount.
I do need the computer now "ish", and I don't need any incremental performance improvement of M3 over M2 for the basic personal stuff I'll be doing on it.
Potential disadvantages in that the M2 would be cheaper when the M3 comes, and perhaps may go end-of-life and not get OS updates for as long in the (relatively far) future. I can live with that.