Hi. I'm OTB USCF 1800 and I currently decided to change most of my opening repertoire. I know you're probably like: "Stop being stupid and just stick with one opening." I have stuck with one opening as White and Black (vs 1 e4 and 1 d4) for about 2 or 3 years now. As white, I play London System (upon my used-to-be-coach's recommendation) and as black, e5 against 1 e4 and semi-slav against 1 d4.

I'm actually okay with sticking to semi-slav and e5. It's the London System that I'm not okay with. Sure the London System makes studying white opening lines really easy but the play is sometimes too equalizing / passive / boring (although chess could never be boring :)). The reason my used-to-be-coach told me to play the London System was because it suited my "style" (many players have told me that it wasn't a compliment). So according to my used-to-be coach, my style is solid, a little bit passive (which I'm trying to work on), and steady. However, I feel like playing the London System has not helped me improve a lot. I used to play e4 Ruy lopez (although I don't know the variations; I just impromptued it). If I switch to e4 then it means I'll have to learn variations against the sicilian, french, etc. And also, I listened to Dan Heisman's Opening Repertoire video on ICC and he said something about playing openings that are the opposite of your style to help you overall.So now, I'm confused about what opening to play as White. Thanks!

The London keeps blunders down and reduces theory. That's all it does... The only other people that use it are very very good endgame players.

You can play whatever you want really. I know a guy that plays the matrix against 1800s and wins all the time and that's pretty funny. What you play depends on what positions you like. But if you are passive it doesn't hurt to change up completly and go super tactical all the time and vice versa. Many people play 1.d4 only to avoid tactics and that's not a good idea while others play 1.e4 to avoid slower games and always drop their d-pawn against the French.

As long as you're not playing openings to avoid weaknesses then it's ok. But if you're bad at something it's better to just fix it now.

Build a 1.d4 Repertoire by Nigel Davies seems like it would be a good fit for you.

He starts out with stuff like the Colle and the London and graduates to stuff with c4

http://www.chessbase-shop.com/en/products/4298

I was in a similar boat until recently; I had been playing the orangutang (1.b4) for nearly two years when I switched in July to 1. e4.  I was initially scared to do so because I thought my results would suffer due to the mountains of theory, but it's been a great experience.  I am really enjoying the variety and quicker paced games.   In the past couple of months I saw my rating jump from 1700otb to the 1800s.  I attribute some of that to my switch as I felt I needed to learn to play and appreciate dynamic chess more.   I think your idea of following Heisman's advice is on point.              

Lol, I also remember him posting a very similar one like half a year ago. I don't think he actually takes any of the advice given, and just impulsively posts the same thread worded differently once in a while...

Aha! - and I was afraid it was a really scary case of déjà vu . . .