I'm confused about the enthusiasm for this so I'm just checking my reasoning here so forgive the questionable clarity.
But, if on an exceptional Tesco deal you can get say 1500 points - or 3600 BA miles for £75.00 worth of wine (which we do sometimes) this makes the BA miles cost 1.94p each against 0.83p for the points via Marriott. But with the purchase you get the wine. Doesn't this mean that whilst the purchase of miles from Marriott is good value compared with the cost of purchase direct from BA, or compared to the cost of a decent purchased flight - you either pay 42% of the Tesco wine cost to Marriot but don't get the wine - or pay the full 100% to Tesco and get the Wine.
I can just about follow what I've said myself so I guess this is tough for others - but doesn't the wine route seem a no brainer if you can get enough transactions through enough accounts to support your travel aspirations?
Have I got the sums and reasoning right or am I off-track completely?