Graded? Nope, can't say I have. I own a lot of collectables but they're too obscure to have much value to anyone who isn't me. Sadly.
Not sure if you will get much value from a grading.The scalpers are the ones that command high prices. People pay them but most people don't believe the high prices are justified. You might get a note back that your dolls are only worth retail. Monster high is still new so i think it's too early for them to actually go up in value for real. One of the reasons why i try to avoid buying them at high prices.
Also in today's market with ebay and such, prices of collectables has kinda plummeted. I notice this in the vintage doll collector groups. What they paid 10 years ago vs what the same thing goes for on Ebay are very different. Back when internet buying was pretty rare, a collector or dealer could effectively name their price. Now the buyer names their price, and that pushes prices down.
I still see some collectors of vintage Sindy trying to sell dolls for £60 or whatever, prices they would have commanded pre Ebay but if I watch the same item on an auction site, it'll go for £40-50 instead.
I base my prices on going rate on Ebay, seems the best way to estimate it. Are some of my dolls valuable? yes, I have a few SDCC exclusive MH dolls and I also own a fair few vintage dolls that are 50 years old and in very good condition, but they're only worth something to the right people and the market is so unpredictable.
Right now for instance, Sindy prices are through the roof compared to what they were 2 years ago. Why? She turned 50 and there was mention in media, getting people interested again. More buyers on the market, particularly new buyers who aren't "in the know" drives up prices.
MH probably will end up collectable, but will it end up valuable? I don't know. Mass produced toys are funny like that. It all depends on how well they survive the test of time I guess. Dolls who don't age well command a higher price for ones in good condition, as most are damaged or destroyed by age related issues. Dolls that were produced in very small quantity will stand up value wise a lot better. But it's still a real guessing game and a gamble. Once mass interest wanes, you're looking at a small community of die hard fanatics and unless the item they're after is particularly scarce, there simply ends up with more supply than there is demand.
Case and point, Planescape. Not a toy, but a series of role playing books for Dungeons and Dragons. As a setting, it was bizzare and as a result, the fans are a small but die hard bunch. A fair few people overlooked it when it was released and yet others just don't like it because it's strange and not really at all like anything else D&D. (It's a setting where you probably SHOULDN'T try to kill stuff, because it'll tear your soul from your body and wear your face as a hat if you try)
Now this does mean a great deal of the books have very little value because they were mass produced and there's not a huge market for 2nd edition D&D books in any event, let alone one of the more obscure settings.
But... the rarer books, the ones published toward the end of the run? Those command a much higher price. And the pewter badges TSR made to be sold in stores? Wowza. I own a half dozen of them and since winning them a good 8 years ago, I haven't seen a SINGLE one pop up on Ebay or any other trading site. They are stupendously rare and the only thing keeping them from selling for insane amounts of money is that it appears to be only myself and one other person on the planet who wants to own them lol.
Supply and demand, and things go in and out of fashion, even collectables.
I consider grading new toys to be a scam perpetrated by grading companies who've run out of Star Wars vintage figures to obsess over.
I don't think I will need them graded I will never sell them, and when I die I want whoever in my family to keep them and look after them I don't think they need graded.