There is no reason to divert just because you will be below alternate fuel at your destination - it's comletely legal to continue and land at destination as long as you land above final reserve. Therefore, if the weather is good and there are no other reasons against it, taking exactly planned block fuel is fine imho. In case of delays burning more than contingency fuel you will just have to take a decision about which airport to commit to land a bit sooner.
And if there are no delays but you arrive at destination below diversion fuel - than the planning was wrong and that's a safety report. A few of those should change the beancounters' mind about proper fuel planning, right?
Of course I don't object to taking extra fuel when needed (weather, temporary situation), but if your experience tells you that you always need those 500kg extra, don't just take it automatically and don't say anything, because the next guy may not have your experience.