I'd still just carry a copy WITH A COPY OF THE ENTRY STAMP. If they run raids 6 times per year and you're only going to be in town for 4 days, that means there is less than a 7% chance there will even be an immigration raid while you are there. Add to that the fact that apparently quite a few guys were in town during this latest one but were NOT at the HDR/BM when this latest episode happened and it becomes even less likely that you'd be at the wrong place at the wrong time even IF a raid went down while you were in town. Add to that the fact that a raid just happened and you are going in just a couple of weeks and the odds that they will have another raid so soon after the last one means that you'd be even less likely than that one would even occur while you'll be there. Add to that the fact that these guys don't really think there are many gringos at these places who are there illegally and are mainly concerned with checking the CHICA's ID's, which are much more likely to turn up illegal aliens (though that may be changing as originally I believe they didn't really bother to check the gringo ID's at all). Of course, this assumes that these raids are relatively evenly spaced rather than done in a back to back fashion and that the number of raids is not on the increase, but I don't think those assumptions would be really that far off. All told, for you, I'm guessing that the odds of a raid going down at one of these places WHILE you are in the bar and you ACTUALLY getting caught up and arrested for not having your actual passport has to be something well under 1%
The above analysis also ignores the possibility of being hassled by the police on the street. Personally, I've NEVER been hassled by police on the street. Maybe I've just been lucky or maybe this is another area that has increased greatly in the last year. I think part of it is not walking around in an area and at a time where your presence might be considered suspect (ie late at night in a noted sex tourism area like the Gulch). Of course, one probably shouldn't be walking around these areas at these times any way for OTHER reasons (ie getting robbed by the criminals on the OTHER side of the law), so if you take cabs between the SL and HDR and other places at night you'll probably also greatly cut down whatever risk there might be of being stopped and hassled by the cops on the street.
In short, despite the more recent developments regarding a copy of your passport photo and stamp pages not being sufficient SOMEtimes for SOME of the cops, IMHO the risk of getting your passport lost or stolen while carrying it around still exceeds the risk that you will get in trouble for only having a copy.A couple of other comments:
1) Were the 3 guys arrested for having illegal drugs on them gringos or ticos? And if they were gringos, what sort of idiot gringo carries around illegal drugs while in a foreign country that has harsh prisons and harsh drug laws like CR AND especially into a bar that is known to have periodic raids?
2) The 3 drug arrests aside, if this raid involving 15 gov't agents only netted ONE chica for illegal immigration (and past raids were similarly unproductive in that regard), isn't that a pretty piss poor use of resources? Perhaps if that ONE chica was dealing drugs or involved with robberies and other crimes I might see where it would still be worthwhile, but this was a chica whose only OTHER "crime" (apart from her illegal immigration status) was being a prostitute (not actually illegal in CR) and taking money from Gringos in exchange for services. She wasn't being trafficked or pimped. She wasn't stealing from anybody or at least wasn't being charged for that. And she had a reasonably steady source of income coming from foreign sources and thus, unlike some other illegal aliens, was not really any sort of drain on the CR economy due to her use of their social welfare system, etc. (unless their concern was that she was competing with tico prostitutes for gringo dollars).
3) IMHO, these raids have NOTHING to do with law enforcement effectiveness and efficiency and have EVERYTHING to do with politics. Do something high profile and dramatic involving the use of many officers and if Canal 7 happens to be along with their cameras to shine their brights lights on this "seedy and disreputable" business of sex tourism then so much the better.

Harass the sex tourism businesses, making it harder for them to conduct business as usual, first by going after the chicas on the flimsy excuse that some of them are here illegally (sort of like going after MP's for fire code violations and not providing wheelchair access), and when that didn't prove to be harassment enough going after the gringo sex tourists themselves even though in virtually all cases their entry documentation winds up being in perfect order, albeit not always actually on them.
4) These spot checks of gringos mainly seem to happen in downtown SJ, particularly around the Gulch, and mainly at night when most of the gringos about in those areas are male sex tourists. Is it because this is a demographic that is more likely to be in the country illegally than other types of gringo tourists? I doubt it. I wonder how many eco-tourist types have been similarly detained elsewhere in CR for "only having a copy of their passport" or even stopped and questioned about it at all (apart from around border areas)? I'm guessing very few if any.