Bored at work and though I'd have a play about with previous festival winners going in again. Results are since 1990.
Overall 77 winners from 563 had previously won at the festival.
The majority of those, as you might expect, came in the 3 Championship races. The Stayers and the Mares features heavily due to a couple of horses (Inglis Drever, Big Bucks and Quevega).
Just looking at the top 4 missing those 2 races out, you have:
[TABLE="width: 246"]
<tbody>[TR]
[TD]Champion Chase
[/TD]
[TD="align: right"]14
[/TD]
[TD]10 x Arkle Trophy, 4 x Champion Chase, 2 x Grand Annual
[/TD]
[/TR]
[TR]
[TD]Champion Hurdle
[/TD]
[TD="align: right"]11
[/TD]
[TD]4 x Champion Hurdle, 6 x Neptune, 2 x Supreme, 1 x Triumph, 1 x County Hurdle
[/TD]
[/TR]
[TR]
[TD]Gold Cup
[/TD]
[TD="align: right"]9
[/TD]
[TD]3 x Gold Cup, 5 x RSA Chase, 1 x Ryanair, 1 x Spa Hurdle
[/TD]
[/TR]
[TR]
[TD]RSA Chase
[/TD]
[TD="align: right"]4
[/TD]
[TD]2 x Spa Hurdle, 1 x Bumper, 1 x Martin Pipe
[/TD]
[/TR]
</tbody>[/TABLE]