It would depend on the reason you are trying this but I agree that it is in most cases not a suitable first trip choice.
Stronger extracts like any above 5-10x are not really different than plain leaf but only more potent. It is harder to gauge a correct dose from any preparation that is considerably potent especially if you eyeball it (guesstimate doses instead of weighing them on a scale).
Consider that mushrooms are generally dosed quite precisely (and it is indeed foolish not to) but why should it be any different with Salvia? Because it lasts for a shorter time? There might be a broader dose range but that doesn't mean it's smart to just randomly put an amount in a pipe and see where it gets you. This is the reason stronger extracts are generally not tolerated so well: they are often put equally casually into a pipe vastly increasing the unpredictability of the outcome.
Though if you are weighing your doses on a milligram scale there is not really a reason why a dose of 30x extract would be that different from a dose double that amount of 15x. There is one difference though: the less potent your extract (or plain leaf) is, the more plant material there is to combust that only serves as a carrier so to speak. So as long as you can weigh accurately stronger extracts would be preferable IMO but above 30x (or even 10x) I don't see the point anymore.
There may be marketing lies as the poster above me said, but when the manufacturer is truthful about the product extracts should be standardized. When they are standardized they should be comparable at the same potencies.
Save the salvia for later and get different drugs first that are more classically psychedelic. Salvia is very a-typical! There is a significant dissociative aspect to it. I found it very confusing and complex though I never had a blast-off breakthrough experience. Actually I just did not find it very helpful in any respect.
After you have tried real psychedelics you could always choose to return to the salvia, but when you do perhaps look into buccal / sublingual dosing instead of smoking.
check out this similar thread:
http://www.bluelight.ru/vb/showthread.php?t=497473