I most certainly have.
A couple of months ago, Gear4Music in York had me comparing a complete mahogany parlour, Martin and Sigma. (00015SM) The main difference being solid v laminate back and sides. To be honest, the Martin wasn't five times the guitar despite being five times the price. In fact, there was little in it.
Granted. Ten years down the line, the Martin will still be improving whilst the Sigma will have peaked not too long after you bought it.
Same rules must apply to the DM ones you are looking at.
I have had a go on the DM18 and liked it. To be honest, I don't think they know how to make a bad guitar. I have often fancied a DR28 on the basis that whilst I will have a Martin again some time, my style of playing means expensive guitars for me tend to be OM/00 so a Martin OM28 if I do get one. I like 'dreads though and a Signa is a bloody good 'dread for the money.
My loose "one in one out" policy means that a 'dread is going to have to be sacrificed for this fan fret I am hanging my nose over. That'll mean I only have one 'dread left. (Although it is solid wood, wonderful sounding, excellent playing and been in my collection since the late '80s, the Jim Harley cedar / ash guitar has to find a new home. The former Mrs Musket bought it me and my Worksop Guardian mouthed son let the fact slip in the wrong company. The poor guitar gets the dead eye by both Mrs Musket and her sycophantic greyhound.