Hi K.,
I know how "open" rooms like that feel, but when you try to decorate it, sometimes you can draw MORE attention to it than if you just left it alone. And, to actually do it "right" it would take alot of $$$$ and a wonderful "crew" and at least the whole day before the shower. So, if $$$, people, and days are no problem..... then I say go for it :O) Hang it, rent it, or whatever...
Now if you are trying to fit about 17 tables, then you can try to take up most of the space and it will look lovely, however, if you're only needing like 6 tables, then you should try to keep the feeling small & quaint. Remember, even though a normal table can fit 10 people, you can make it more comfortable by keeping it at 8 per table, then you will have more tables and using your space better :O)
In my opinion, I would focus on the section you ARE going to use and try to have them facing your guest of Honor. Have your Cake & Gift tables near your Guest of Honor so your guests are never noticing the whole space. Your guests will know it's there, but it won't be a big deal, I promise.
As far as "re-usable" gifts.....You can make a "Diaper Cake" for the center of each table. This way your new Mommy will have lots of diapers. I always decorate my "cakes" with a bib, rattle, a onsie, or washclothes and booties. Then add some ribbon or a bow on top. It's VERY cute, and I have a "recipe" for the Cake if you want to see it. All you need are Newborn Diapers, and rubber bands, then whatever you want to put on the "cakes" :o) This an be expensive, too, but if you have a group of people "going in on decorations", then this IS their gift, so they don't have to buy anything else.
As far as gifts/prizes for games to your guests, I would buy 2 Bunches of flowers from Costco and split them up into 3-4 bunches depending on how many games you are playing. The Dollar Store always has great vases to put your flowers in. Put these flowers as decorations on your Gift, Cake, Entry, and Mommy's tables. They could be used as decorations AND prizes.
Oh Yeah, if you don't have a group of people wanting to help, then don't forget to ask for help.....I am sure that there are alot of other women who will help you BUY and PREPARE for this shower, so don't exhaust yourself!
Have Fun, K.!
~N.