As I understand it you can burn your diversion fuel flying towards your destination if it fullfils a minimum criteria of vis minima, two runways available + no expected delays
Just to correct a point, two runways are NOT required when deciding to burn your alternate fuel once you are airbourne. Two runways are only required when PLANNING a flight without an alternate.
The requirements are:
At your destination aerodrome an EAT has been issued, or the delay is known or no significant delay is expected (<20mins)
You must be able to complete an approach in the event of any forecast weather deterioration in conjunction with a single failure of groung OR airbourne equipment that would downgrade the landing capability of the aircraft.
The commander has taken into account the traffic and operarational conditions at the destination, on the route to the alternate and at the alternate when deciding to land at the destination or divert so as to land with not less than final reserve.
As I said in a earlier post this gives the skipper a good deal of flexibility when deciding how to use the remaining fuel and he/she can use thier own judgement as to what is a good idea and what is not which I rather like.
It seems to me that most of these decisions can really only be made once you are at your destination or very close to it. The second regulation is really the only one that you can look at in advance, the other two need up to the minute information about what is going on at the time. If you are some way from your destination and you continue knowing that you are going to arrive without the ability to divert you are really backing yourself into a corner and may start to run out of options very rapidly.