EXECUTIVE SUMMARY:
1) Usually no need to prebook.
2) Traditional "Highlights" (aka "All-in-One") Tour no longer offered due to last year's earthquake.
3) IMHO, no big deal on the loss of the Sarapiqui and Braulio Carrillo parts of the original Highlights Tour, but not sure what if anything has replaced them.
4) Poas/La Paz combos are readily available (see link for one below)
5) Poas and Doka make for another combination which might be even better (if you save La Paz for a day of its own)
6) IMHO, "Multi-Combi" tours that try to do too much are fine for those with only a few days in SJ AND who don't ever expect to return, but most mongers should have plenty of opportunities to see all of these attractions at a more leisurely enjoyable pace.
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1) Orange is right. No need ever to prebook any CR tour unless perhaps you're getting into CR after the tour offices close and want to go on a tour that leaves early the next morning.
2) Also, some people are still talking about the 4-in-1 tour like it even still exists in the format they remember. There was a major earthquake in that area that completely closed La Paz Park for several months. It has since recently reopened.
HOWEVER, the road between La Paz and San Miguel (which is on the way between La Paz and PV de Sarapiqui) was also closed and is expected to remain so for the foreseeable future, so the "Highlights Tour" that most people remember and have described is no longer really even being offered. In order to travel between those 2 points one currently has to either drive all the way around the far side of the Poas Volcano through San Carlos (Ciudad Quesada) or all the way around the Barva Volcano through SJ and Braulio Carillo (which is the way you'd come back to SJ). And neither of those routes are at all practical as part of a day trip package.
3) I'm not sure what, if any, substitutes they might have come up with to fill the place that had been filled with the Sarapiqui boat trip and the return drive through Braulio Carillo, but those were, IMHO, the weakest part of the tour anyway and what really made it such a long and tiring day.
4) Besides, although your thread title says "All in one", all your post was asking about was La Paz and a volcano together anyway. And there are lots of tour companies that combine just those 2 attractions. Just do a web search to find some or inquire at the hotel tour desk after you arrive. Here is just one link I found with a quick Google search:
http://www.costaricantrails.com/tours/san-jose/poas-volcano-la-paz-waterfalls2.html
La Paz and Poas make for a good combination because, like other volcanos, Poas usually clouds up around mid-morning eliminating the views that one goes up there for. So you can rise early, hit the volcano for an hour or two and still make it over to La Paz by the time their own tour buses even arrive from SJ.
5) If you're really interested in some of the other attractions included on the "All in one" Tour, you could also combine Poas with a visit to the very interesting Doka Estates coffee farm. Their own website includes a combo tour with Poas which they call the "Estate Peaberry AA" (see:
http://www.dokaestate.com/coffee_tour/schedule.html). And, in fact, might make more sense than the Poas-La Paz combo. The reason I say that is because Poas and Doka by themselves are at best half day tours with only an hour or 2 normally spent at each location (not including any meal stops), so together they make for a more natural combination that still gets you back to SJ fairly early (in time for an afternoon MP session). Poas and La Paz would make for a manageable but somewhat more full day. Besides La Paz can make for a nearly full day just by itself, with a late pickup between 10-11AM (which many would appreciate since it allows you to sleep late) and a return to SJ between 3-4PM. So you'd be splitting things up more evenly if you did Poas and Doka one day and La Paz on another.
6) OTOH, if you really still want to squeeze "everything" into just one day, there are also other "multi" or "combi" tours that combine various attractions though they fall a little short of the original "All in one". For example, while the "All in one" may no longer be available it is probably still possible to go on a tour that combines Poas, La Paz and a coffee farm and tours that combine Poas with visit to western villages such as Sarchi and Grecia are also available. Personally, IMHO, unless you only have 2-3 days for tours and NEVER expect to return to the SJ area, I think you're often better off splitting things up than trying to squeeze everything into just one day (I've only done the 5-in-1's myself when I've been taking first and only CR trip travel companions). First of all, a 13 hour long tour day means arising really early and getting back really late which, in turn means you'll be fairly tired to fully enjoy any night-time P4P activities and won't have any time at all to squeeze in any daytime ones. Plus, the more tours try to do in one day usually the least well will they cover it, with sometimes very perfunctory stops at some of the attractions. But obviously these All-in-One tours are still also highly popular even with some vets, so YMMV.