Case study: You're not comfortable with the level of effort your staff is putting forth lately. You get the urge to give the "it's your restaurant too" speech. Is it a good idea?
I don't know if I'd want my staff thinking they owned my restaurant. While it's nice to think we can motivate people to behave like they owned the place, without actually owning some place, they simply can't know how to behave that way. Most employees see owners as lazy, and as someone whose job they could easily do, mainly because they have no clue what their job is.
If you are really looking to get something done that isn't getting done, the way to do it is through your systems. Add it as someone's job. That way you'll never have the "It's not my job!" excuse. When someone uses that line, the first thing to do to combat that attitude is to make whatever it is you are talking about part of their regular duties. That way, when they say "It's not my job!", you can come back with, "It is now.". The next time they see something that needs done, but it isn't their job, they'll be that much more likely to take care of it that one time so it's not made a permanent duty of theirs.
If you are looking to make your employees understand better what it means to be an owner, make them see the financial picture in your restaurant. Play the "restaurant game".
Have a staff meeting and hand each of the employees $100, representing your sales. Tell them you are going to let them know what it is like to be in the restaurant business. Talk to them about each of your expenses one by one, and take away a portion of their $100 to signify what you pay for each of those expenses. By the time you take $35 to pay for food, $30 to pay for their wages, $12 to pay your rent and occupancy costs, then dollar after dollar for each of your other expenses and taxes until they are left with $4 or so, if anything, they'll start to get the picture of what it is you go through. If you are loosing money, this is even more effective because you can ask them to pay you after you take all their $100.
Getting your employees to empathize with you is a very powerful motivation tool, especially if they understand that the more money you make, the more money you have to pay them. Further explaining how seemingly little actions, like helping to make sure the restaurant's appearance is up to par, directly or indirectly effect profitability will help to motivate them to consider things outside of their normal job descriptions to help you, and in turn them, become more profitable.
I don't think I would want my employees thinking they owned my restaurant. That's like letting the patients think they own the asylum.