Unfortunately I think this recipe needs some work, but I'm not sure I can help much. I did do some experimentation with some of it. I poured out small measured amounts of the beer and then added measured amounts of vanilla extract. This was just store bought vanilla extract, so we aren't talking anything special. I ended up coming up with needing an additional ~5.8% vanilla extract to get a big vanilla taste. So I took a few bottles I had, opened them up, removed about 0.7 oz of beer and replaced it with 0.7 oz of vanilla extract. I did this probably a year ago and I've probably had 1 or 2 since. I'm not going to lie and say it's a great beer or a clone, but it made it better as it covered up some of the spiciness from the cardamom and greatly boosted the vanilla flavor.
So, as for how I'd change the recipe, I would almost start with 1/10 the level of cardamom listed in the BYO recipe. You can always add more, but you can't take it away. Although I do remember it being pretty expensive as I had to buy a whole jar of it, so unless you already have it in your spice rack, I would just be tempted to remove it.
As for other changes, I would say you need to up the lactose and vanilla a lot. I'd be tempted to use some beans and some vanilla extract as it's going to get expensive quick if you use something like 10 vanilla beans. Up to you though.
It's been awhile since I had the real thing, but I also think it's super sweet. Mine did finish at 1.038, so it's sweet, but I almost feel like it should be sweeter. I've never tried it, but I thought I read that some people will back sweeten with splenda. Might be worth a shot.
So with all that said, I can't see myself trying to brew this beer. While I love this beer, I don't love drinking a lot of it and it seems like it will be tough to recreate what they've done. I assume they just load it up with some high quality flavor extracts that we don't have access to and that's why it doesn't taste artificial despite using flavor extracts. Good luck if you do try to clone it and let me know the results as you may make me change my mind about brewing it again.