I was a member of a wood turning club a few years back. We ran into similar problems. Stagnant growth, meetings generally turned into show and tell, and not much else. The straw that broke the camel's back for me was that the solution some came up with was to greatly increase dues and bring more professional presenters in. I was on a limited budget at the time and the increased dues would have pushed me over the edge of what I got out of the club. It was the breaking point for many others as well, and we left.
The point is, in order to attract new members, you have to have activities that will keep up the interest, and have some variety. With a photography club, the obvious choice to me is to organize outings. I assume that is the "photo walk" you refer to. Those could be a real draw, if there are those willing to put the work in to organize them and make them interesting experiences. A "photography walk" to me sounds more like an impromptu walk through a nearby area looking for interesting subjects. I'm thinking more about full fledged outings to areas of interest that offer excellent photo opportunities. Depending on your area, that could be a tough row to hoe after picking all the low hanging fruit. You also run into burnout on the part of those that are willing to step up and do the heavy lifting of planning and carrying out the outings.
One suggestion I would make is to try and bump up the presentations at the monthly meetings. The presenters don't have to be experts in the technique presented (heck I made several presentations at our turning club), but they do need to be prepared and do their best with a technique/subject that they have some facility with. Obviously there will be those in the club with more experience and talent, and those that are either just learning, or don't have as much talent or interest. Still, everyone should be able to take something from a well prepared presentation.
I would advise against making restrictive rules. In my experience it merely leads to driving off some of the folks that you may be able to draw in to the core membership. I'm not saying you should cater to the every whim of those on the periphery, but restrictive rules and expectations can be off putting to those you are hoping to increase your numbers with.
The other thing is to advertise. I'm not talking about buying a spot on the local TV station, but there are ways to get the message out that you have a photography club and are looking for new members. Flyers on bulletin boards at libraries, work places, senior citizen centers etc. Perhaps you could contact the local newspaper about doing an article on your club. Some radio stations will broadcast information on local clubs and charities. And of course, word of mouth by the members can be a great way to spread the word. Advertising some of the more attractive photo outings to non members might be a great way to bring new members into the club.