The test of good philosophy for me is how concisely and how easily the concepts involved can be explained in plain english, with the minimum level of abstraction. This is a problem in philosophies that involve some requirement that sits above or beyond the sphere of human experience. It's important to remember that human experience doesn't only comprise those things that are demonstrably real. We (as cognitive beings) are as much a product of our notions whether they are factual or fabricated, real or imagined. What philosophy is required to do is provide meaning to us on a wide scale and where this is not possible then there is a good chance that we've fallen into the realm of self gratification on the philosopher's part. Some branches of philosophy are near incommunicable. When you ask a man to cognitively process something that is allegedly unknowable then how can you ever really expect him to understand the point you are trying to make? Without some relevance to things that we have experienced does it even matter? If Noumena are beyond the grasp of humanity then logically it is impossible to probe or test their existence even in purely philosophical terms. Platonism has a similar issue - where there a perfect ideal of every thing from which all other things are described but this idyllic, essential form is naturally unachievable. It cannot exist.
Though I suppose Platonism has the benefit that we can extrapolate perfection from imperfection; and while it may not be an achievable goal it is ever something to strive towards.