I Should've Been a Yenta

Here's the awkward scenario-- I know I'm not the only one who's been through it, so any advice would be appreciated:
Friend from one part of my life meets and has amorous feelings for acquaintance from other part of life. Friend wants me to celebrate. I want to vomit. No, nothing that harsh, but this has disaster written all over it.
Hmm... vague. Let me try again.
So there's this person I absolutely love and hold in the highest regard. He is one of my great platonic loves. There is an unparalleled goodness in him. Never have I known someone so loving and attentive and sweet and humble and compassionate. He sees only the good in people and makes everyone around him feel like gold. He walks into the room and the world is bright. He makes you want to be better, because he treats you like you are already there.
Now before anyone (ahem, Grant) goes about assuming I'm gone for this young man, let me set the record straight-- I'm not. It's really a strange thing, because he's better than anyone I've ever picked out for myself, but my love for him is sisterly. In the spirit of full disclosure, there was once a kissing episode, and while it was good for my pride to be publicly kissed by someone so handsome, it felt ooky, and immediately after I went and kissed my old boyfriend at the gas station.
Anyway, I got an email from this friend saying he met someone I know. He's supposed to call. All I can do is pray he doesn't ask me for my honest opinion.
What do you do when your friends are going down that path? Oy.
When another friend I know and love called me to tell me she was engaged a while back, I tried to be supportive. I went that route. I thought the fiancee sounded sketchy and the courtship too brief and it felt like it had disaster written all over it. But she was so happy, and had wanted this kind of "love" for so long, I didn't want to rain on her parade. I went with the whole, "All I care about is your happiness" line-- not endorsing the relationship, but not dogging the guy either. Turns out he was a jerk (and creepy, and MARRIED), and it all ended before she could get even more hurt (believe me, she was hurt enough). But I couldn't, nor WOULD I ever, tell her "I told you so." I hated her sorrow and tears, wanted to shank the butt munch, and said a little prayer of thanks as I breathed that proverbial sigh of relief.
One time, when I was going out with someone a little evil, I remember my one of my best friends saying, "I can't say anything, because then if you marry him, you'll always remember it." It took a while for me to fully comprehend how right she was to allude to her dislike. This may be an appropriate track. I only wish I would have thought more about her talent for discernment and heeded that warning before I wasted months and months on the so-called rack of love.
My out-of-this-world friend could do so much better than this Mediocre Mary. I don't want to be a hater, but let's just say she is yucky and I don't really deem her worthy of him. And I know it's not my place to say anything, nor is it my place to arrange a marriage for him. But I wish it were.
As a matter of fact, I sometimes think I missed my life calling. Not that being the Queen of Insulation isn't fulfilling-- it so is, but I would be an excellent matchmaker. If it were up to me, I could help orchestrate lovely relationships for people, and save everyone the headaches and heartaches of love gone bad. Now, I'm not saying it wouldn't be a challenge. I tend to want to marry all my good friends off to people at their level, but there does appear to be a shortage of suitable prospects around. But think of how much trouble it would save! No more twist of the knife in my lower abdomen when I find out my friend's crush already has a gf. No more weird jealousy when this one girl I think is pretty cool consistently texts me asking me for my own love interests' phone numbers. I wish I could shake my really good friend and tell her that the guy who cheated on her a while back is nasty and she can do much better-- and she'd actually believe me. I could shake my other friend who still feels bad about how this jerky hoser treated her, and help her find someone who would treat her well and not mess with her feelings. I'd kick all those little menaces out of the running-- the ones who think none of my girls are up to their level, the ones who sit sulking in the corner, the ones who can't get a job but still think they're the shiz, etc., etc. I'd use a magic mirror to show my lovable (yet clueless) boy friends how truly beautiful some women are, and the awfulness of others. Sometimes outsides and insides go together, but often they do not.
But what can you do? God doesn't take away our agency, and I certainly don't have His level of power to enforce my will and good sense on others. We all have our own taste and preferences and idiosyncrasies and that's what makes the world go round. But if you're a dude and looking to be set up, ask me about my beautiful, wonderful friends. I'm not going to steer you wrong. And if you're a girl, believe me, I'm working on it for you. There are great guys out there. They just get distracted by roadside attractions. The advertising is appealing, but at the end of the day, you're still just looking at the world's largest (potato) flake.