Hi
If your happy with your ambient light photography then be happy with it, however.
i'd just like to add, Apart from the above, EVERY shot benefits from FLASH photography not just macro photo's.
Most of us use flash to perfect what we call, wideangle balanced light, quite simply adding flash to an amount which will capture natural looking tones and colours and to revel textures in our subjects.
Granted, if you can't get close enough to you subject, but we all suffer this from time to time, however, there always comes a time when we get close enough and coupled with just the correct amount of flash we can produced stunning results.
Below is a typical example of a Balanced light shot, If i was not to add flash to the foreground of this picture, the turtle in the shot would have looked ok, but, his true colours would'nt shine through.
instead what i've ended up with is a shot that show's just how perfectly the average turtle can blend into his surrounds. not a master peice, but it shows the true colours of the reef and the creature

another one below again a turtle, but its balanced against a sunburst, if i shot without flash, we simply would have ended up with a silouette shot, which still would be nice, but, the fill light adds impact to this shot

Get yourself a couple of Strobes, you want be dissapointed.
another item you could look at is Alex's Magic Fliters. but you need to shoot correctly and using the sun correctly to acheive good results with them, but they are excellent
regards
craig