No, you're not missing a trick. A £1.98 pudding gets you 120 BA Miles, although that is not a great deal in itself unless you really want the pudding! The Johnsons deal was substantially better because you were spending £1.44 to get 240 BA Miles which is exceptionally good value and worth buying (and binning) the talc for.

Some people redeem Tesco vouchers for Tesco Deals instead, where a 250 points gets you £10 towards a Virgin Holiday, RAC membership, a new car etc. These can offer good value, but if this is your focus then you'll find the discussion over at paidtoshop.co.uk more useful as those guys discuss Tesco Deals heavily. We don't, normally, because most of us transfer to BA Miles so the focus in this thread is on earning rather than spending.

PS. If you've got a stack of Priority Club points, make sure you also check out the Priority Club board - and, in particular, the current offer of 50% off the 'Anyhotel, Anytime' giftcards which is a great deal.