So, I'm admittedly a bit "old school" in that I like choirs and orchestras WITH the traditional praise band. You don't see orchestras hardly at all in Colorado churches and choirs themselves are disappearing too. As an artist and a musician, I worry about "art" disappearing in our church culture. As a result of orchestras and choirs going the way of the dodo, worship leaders themselves are often only part-time and fewer and fewer are ordained ministers or even attend seminary.
I understand the mindset of removing choirs and orchestras from the church is because 1. there are fewer people trained in how to direct these groups and 2. the modern generation appears to want only a "rock concert" or "band" ensemble as it more resembles what they listen to on the radio. Like I said earlier, I worry that "art" is disappearing from our church, but I think that's only part of the issue...
..In fact, I don't think it's "art" that is necessarily disappearing, but rather our (American's) standards for art are so high that only professional venues and studios can provide it. Contemporary worship songs still use a smattering of strings and brass, but you won't generally see them in a church service because it is HARD to play those instruments (not to mention that orchestral instruments and choir also need written sheet music to follow whereas a band can play by ear with only a lead sheet to reference).
I have found opening up a music ministry to include other "non-band" instrumentalists and vocalists for a choir provide ways for more members of the congregation to get involved, making the worship service more cooperative and interactive. Still, it's a slow process in getting people to join up (especially instrumentalists!) and I sometimes wonder if I'm misguided in trying to grow the ministry I serve.
I also look for ways to open up the church building for musicians outside of the church to use: piano recitals, concert band and/or choir concerts, etc.
Still, perhaps the preference of the modern church-goer is such that all they want is simple.
I would lend towards using an orchestra and choir SOMETIMES. Every Sunday could be a bit much... but depends on your church. What works for one church doesn't always work for the next. So there's no solid black/white or right/wrong answers on topics like this. My main instrument is saxophone and I grew up playing it in the church. Never in a formal orchestra type setting though. It was always your contemporary worship band structure with a couple of added in wind instruments just doing their thing. :) That only works though when you have musicians that know what they're doing... and know when it's appropriate to play and when they need to put their horn down for a bit. Most don't seem to know that... and most seem to think that just playing the melody the whole time on every song on their trumpet is cool. Sorry... but it's not.
When horns can ADD to the overall sound, it can be very cool. It takes a LOT of time and organization to make that happen though. So if you have the people to pull it off and the time to organize it, then go for it! But again, people have to know (and be okay with) that their instrument isn't necessary on EVERY song.