This is my situation with no trees. Currently using the device pictured with a 70' end fed wire sloping from about 25' to 10' (kids play fort toward the back deck) . Yellow line is the 70' wire. Red lines are power lines. Would I possibly see improvement with a cobweb antenna such as the MFJ-1835 at 25' ? 

I have no personal experience with the "Cobweb" antenna but the design is relatively simple. IMHO, you should have better performance on 20-10m bands as long as you raise the antenna at least 35 ft above ground.
Obviously you will lose coverage on 40 and 80 meters. End-fed antennas are nice and easy to deploy but they are not known for superior performance. It's a great compromise antenna for stealthy installations or for quick deployment in field conditions. BTW, I'm sure you know this but it's worth mentioning since your antenna is attached to the kids playhouse. End-fed antennas can develop very high voltages and should be kept from being accidentally touched, especially near the end.

Can you install a ground mounted vertical in your backyard? If yes, look at "Butternut" multi-band verticals. I've had one that covered 80-10 meters. It worked very well, especially for DX due to it's low radiation angle. It will require at least a dozen radials than can be placed on the ground and fixed in place with small plastic clips to keep the wires from being cut with a lawn mover. For ground mounted verticals, the radial's length is not as critical as for above ground applications. I think "Butternut" sells a radials kit with multiple elements cut to optimum length to cover all bands.

"Spiderbeam" is another great choice if you can install a 33 ft mast and have a rotator. The antenna is light enough to be turned with a TV rotator but it performs very well.

Thanks for the info. Ground mounted vertical is probably out for now due to landscaping projects that will be happening soon so something without radials would be better for now. The kids playhouse is no longer used for that purpose (mainly used now to hold up an antenna mast) but thanks for the safety reminder. You can never be too safe. I'm wanting something for 20m and up and I will just keep my current setup which does ok for 40 & 80. Everything is a compromise but at least I am having fun and always learning. On a side note, I'm not sure what happened to my pictures. Not at home at the moment where I can try to put them back in.

Thanks again for the help.