An interesting discussion. I think a distinction needs to be made between the clue and the entry. For me, good wordplay does not require recourse to reference sources. The entry, on the other hand may need checking. Of course, what makes accessible wordplay depends on each solver's vocabulary and general knowledge but, on the whole, the Times crossword follows this model, assuming a well-educated, well-read solver with a broad general knowledge.
Certainly, the crosswords that I enjoy most are those where the challenge lies in the skill and wit of the clue's construction. I can do them in the garden or in the bath and check any unfamiliar entries later.
Whether solvers choose to use aids is entirely up to them. The only problem is the prize element. In these days of online resources, I do not understand why anyone would bother to submit a solution.