New to the forum, and also new to flying anything other than the cheapest fare, so please forgive me if this isn't posted right.

I'm making semi regular last minute trips from YYZ to Bogota (6 hour red eye flight, Airbus A330-300). The prices when I booked were (CAD):

Flex economy: $928
Lowest premium economy: $719
Lowest business: $2089
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Economy is usually almost full, premium economy mostly full, business basically empty.

I purchased a Premium Economy ticket and a check-in was offered an upgrade to Business for $344.

I took the offer the first time as I'd never flown business before, for the novelty. My questions are:

1 - I assume this is a good upgrade price? Lower than I've seen on some shorter flights before. To be honest I only found the benefit to be fairly small, since I slept for most of it and I have no trouble sleeping in a Premium Economy seat and had nothing urgent the next morning.
2 - Since prices have been exactly the same multiple times in a row, is it more cost effective to purchase an Economy ticket and upgrade to Business? ... If I purchase my ticket earlier and Economy is cheaper than Premium Economy, that is.

Thanks!