Is it possible to add this parameter to vray dirt map. In some cases I find dirt (occlusion) not to be strong enough, so I am forced to find tricky ways to make the effect more pronounced.
Thanks.
You can pipe it through an Output map and use its Output curve to adjust the result as you wish.
Best regards,
Vlado
a simple multiplier value would be nice though 
also, is there no way to multiply a material over another using vray blend?
No, V-Ray does not support multiplication of materials… (it’s not quite clear how to multiply two hilights, for example - they are HDR values and the result would be a hilight squared, which does not make much sense).
Best regards,
Vlado
Just pipe a VRay color into the corresponding slot, and raise its RGB mult above 1.
That though would likely lead to longer rendertimes (due to the wider gap between occluded and non occluded, and the harder time AA would have with those)
Otherwise, and it’s likely even better, use any way you wish to output the AO as a separate pass, and do the goodness in post.