I like Cafe Del Rey for your situation as well. It's about three or four blocks in walking distance to the southeast from where you're meeting them. Cafe Del Rey fits both of your requirements well, and I think your clients will be very impressed, especially if they haven't been there either.
Joe's probably has the best reputation of all restaurants within a 1 1/2-mile radius of where you're meeting. I really like Joe's but I think you'll like the layout better at Cafe Del Rey. Joe's has a lot of style, great great food, a great bar and wine list, but I think Cafe Del Rey's dining room just feels better for folks who are meeting somewhere on neutral ground...
If you feel like getting out of Marina Del Rey, head over to Avenue in Manhattan Beach, about 30 steps from the beach and Manhattan Beach pier. Excellent food!
Or, Joes in Venice, in the beautiful neighborhood of Abbott Kinney.
1023 Abbot Kinney Blvd.
Venice, CA 90291
There is no close comparison -- Cafe Del Rey on the Marina. They have a website. The room has levels so you don't need to be against the window to have a nice view. Good wine list, the chef has gotten a bit frou frou but you still can find good things to eat and they know good service. cafedelreymarina.com is what i have as the website.