I don't see anything wrong with rewarding good work...
It gives positive attention to those who do work, encouraging them to carry on, and letting them know it's appreciated- in class, attention so often falls upon those who're misbehaving, it's nice to recognise those who do behave and try- and a bit of encouragement can go a long way to life-long motivation.
I remember having a system in Infant School, whereby every class had a number of bricks they could earn a day- you gained one for each 'thing' on the list, like lunchtime behaviour, so all classes had a fair opportunity to gain the numbers of bricks. At the end of the week, the class with the most bricks overall would win, and they could choose a fun reward- a turn on the adventure playground, a day in non-uniform, a new book for the class, we even got a wormery once [we asked for a class pet!]... it encouraged the class to work together, and was far more long lasting than sweets.
We also had a table system in Year 2, whereby the best table won a little plastic animal- probably more expensive in the long run than sweets, but excellent nonetheless- you gained something you could keep and collect, and picking the coolest, brightly coloured animals was such a reward!
We had the 'Gold Book' too, where a student from each class was recognised weekly, and given a certificate...
In year 4, we were given stickers, with words such as "wow" on, for good work- in the book, and it genuinely encouraged us to try our best, to earn the stickers- they were given when you'd done work to a standard that was excellent for you, and you'd done your best. It was portrayed as an honour to get one, and a word would be picked to match your work... I remember the excitement of opening your book to find one!
We also had a behaviour thing in Junior school, where the best behaved class member was allowed to take home over the weekend, and have with them during the week, a specific cuddly toy- and the recognition was brilliant.
I think it comes down, in part, to children of an age needing recognition of their work- as a 15 year old, I recognise, good work gets good grades, and will get me a good Uni course, etc- but at the age or 8, you don't comprehend that...
I'm sure people can remember being rewarded for things, and encouraged, and I believe that's what leads to motivation later on- knowing deep down, that there is a point to working hard!
Sweets, of course, have been used- the memorable case of the teacher who used a system whereby if you got through the afternoon without making her lose it, you were given a minstrel- that's not good, because you should be expected to behave to a degree...
I don't agree with using sweets as bribery, or bribing students to behave...
I believe longer lasting rewards are better than sweets, they may be cheap, but it creates, in part, unhealthy associations with food, to begin with...
But I totally agree with the concept of rewarding students.
And as for stickers? There's a reason those in my French class through Year 10 & 11 learnt their vocabulary every few weeks, namely the stickers you got for getting full marks on the test! :P