Well as someone who owned that series of speakers for many years. I had Mon 7's , 9's, CC350, Mini's I used as rears for over decade, until just days ago. That is a very fine setup , you did great buying it back then.
I think yes it is important to match ALL speakers to same drivers and tweeters, basically staying in the same line. I have studio 100's, 570 and studio 20's all v3. When I just days ago changed the rears from mini monitors to Studio 20's. I noticed a difference instantly. The mini didn't sound bad at all to me, but now with the 20's I can hear the setup sing back and forth as things pan around , it matches so so clearly now. I think in some ways maybe Audyssey has a lot to do with it now. Back in the day I did some testing myself and thought it was fine. But I think maybe now that lossless 5.1 the rears have gotten more powerful and have much more going on in them perhaps so combine that with Audyssey and you can now really tell if they're not matched. That's my thoughts after upgrading several times over 15 years. I've had studio series for last 8 years and had monitor series for 8 too basically.
Now also is the studio series better than the monitor series. Well yea it is, I think that much is clear. But with current prices I think you'd REALLY really have to care about getting quality out of your setup to spend the kind of money the new studio line would cost. Monitors are good setup for almost anyone. Only someone really really wanting to take it to the next level would I tell them to spend the money to upgrade. They are much more expensive than when I bought mine. I brand new got studio 100's for $1800, they now cost what $3000 a pair...ouch. Partly inflation maybe, partly the US dollar has tanked and now unlike then the Canadian dollar is worth more slightly so that effects what they need to charge because of exchange rate.
So well hope this helps some and I do LOVE my studio setup. I'd love to have sig setup but I'm not sure I'd ever spend the money to go there.
Marantz 7702MKII/Outlaw 7140 65" 4k Samsung KS8000
i7 4770K/16 gig 2133/970's SLI 840 PRO SSD
Paradigm Studio v3 100/570/20's/2200 Sub