Lets see if I can keep this thorough and yet succint (as most of you know I'm not too good at that).
1) Despite the impression you may have gotten I think most of the guys on this board are into seeing the country as well as the simple mongering. They just might talk about the mongering aspects more because that is what this board specializes in. You should just check through the non-gulch and restaurant sections for starters to find some non-mongering info that is as good or better than most mainstream CR travel forums. There are probably some guys who just go to CR for the mongering but I agree with you that is a real waste. All the other things are what makes CR special and if mongering is all you want there are probably better places for just that, IMHO.
2) If you want to have something lined up in advance given your limited time. An escort agency might be your best bet. Be careful which one you go with. G&G is the one that seems to have the best reputation around here. Just do a search for "G&G". However, there are drawbacks to this approach. Read on.
3) If you are going to spend more than a day or two with a chica, personal chemistry will be just as important as how she looks. That's one drawback to pre-booking an escort. If you don't have a chica you've aready been with on a previous trip, it is best to allot at least a day or two to screen candidates and that will mean you'll have to spend at least a day or two of your 5 in SJ. Otherwise be prepared to send the chica home early if she starts to get on your nerves. This has been posted about extensively elsewhere here, but I couldn't suggest for you a search word.
4) As jimmydr said, many ticas, or at least the "working girl" types from poor backgrounds or G&G girls, have surprisingly poor knowledge of their own country. If they've spent any time at all outside the central valley it has been to travel home by bus or in the passenger seat of one of your fellow gringo tourists. If they have one thing other than pu*sy to offer some gringos it is knowledge of the local language and you've already got that covered. A professional driver would probably have more guide skills than any of these girls, since he's driven the roads and is more in the habit of taking gringos out to the country than the chicas.
5) I also like to rent a car, especially if I have someone else to split the costs with. If you've driven in those other countries, you should not have any problem driving solo in CR. Another route you might consider, especially since you are a more seasoned CA/SA traveler, is to take public buses, which are very good in CR and an excellent way to meet locals.
6) 5 days is not much time at all to see much of CR. You might consider doing what I did on my last trip. I took the bus to Monteverde, spent 2 nights there, and then took the horse-boat-jeep trip across Lake Arenal to the Arenal Volcano/La Fortuna area for a night or 2 and then a bus back to SJ. That would take you to 2 especially nice areas of CR and still leave you a night or 2 in SJ for sampling the local ladies. You could take a chica with you on such a trip, but make sure she's up for some of the same activities as you and be prepared to pay for participation in those as well. Alternatively if you're a beach person you could rent a car, take a bus, take a shuttle or even fly to either coast (Quepos/MA on the Pacific, Cahuita/PV on the Caribbean or fly to Guanacaste). Jaco does not have nearly as nice of a beach (IMHO) but you don't have to take your entertainment with you since it has a respectable P4P nightlife. Don't try to do it all and figure you'll want to come back.
7)Something to consider is a former Oasis and ZB girl named Shirley, who some around here might know, that is now in the guide business. She saved up the money she earned at the MP's and bought a Mitsubishi Montero and is now studying to be a guide. Ya gotta respect a girl like that as so many have nothing to show for it at the end. Anyway she is now offering GFE guide services for $200/day including the car which would probably set you back close to $100/day by itself after tax and insurance. Compare that to G&G which costs the $200/day just for the girl. Anyway here is some info posted at ISG:
"Shirley will be your guide and GFE for $200 per day. She is fun, athletic, speaks some English, and has lots of pretty friends. She is studying to be a SCUBA instructor and guide. She sometimes works the BM. She is about 5'2" nice build, a little pudgy around the tummy, very affectionate but not possessive. Has a great sense of humor.
She has a Mitsubishi Montero that seats four comfortably. It's a little ratty but runs well. This SUV would cost you about $100 a day to rent yourself, with insurance.....
If you are gonna park yourself in Gringo Gulch and stay there, it is not worth having a car, because you can get anywhere in the Centro in a cab for $3.
However, you should know that Costa Rica is a beautiful country, and San Jose is the ugliest part. If you want to get out of town, go to Jaco, Poas Volcano, etc., this is an excellent deal. If you are coming into CR for the first time, this is also an excellent deal for the first night, as Shirley can come pick you up, in lieu of the $20 cab, show you around, and stay the night for $200, then you can decide to stay with her, meet one of her friends, or go independent. Anyway, you are welcome to call her yourselves, at (011-506 from the USA, then) 381-9091. This is her cellphone, and it costs her to receive calls, so please be nice and don't waste her time. http://www.internationalsexguide.info/forum/attachment.php?attachmentid=30665