Just taken delivery of 1.8 Sport last week and part of my deal was to get co-ax speakers fitted in front and the back....the car is great really enjoying driving it
Everyone will hear things differently for sure, but I've been very impressed by the upgraded speakers......I've paid good money on previous cars for decent speakers \ headunit and this is really pretty decent compared to my old VW Golf........I'm sure added amplification would help further and some will want everything upgraded and if you have the time\inclination to do so then it'd prob be well worthwhile.
I've some fairly well specced seperates I use at home that cost a few grand collectively, so I appreciate decent sound when i hear it..........and I've been pleasently surprised by the sound produced in the civic with the dealer fit co-ax....feels solid and I've absolutely no complaints. My missus said last night how much better it sounds than the golf, so it must be fairly decent for her to say so.
Infinity make very good speakers for sure, but it's all down to yourself and whether you want to simply pick up your car with all the prep done, or get get someone else \ yourself to kit after taking delivery.............either way it will be better than the standard cones...which are not the best IMHO.
If my dealer had not been as cooperative in the deal I'd have gone for an infinity install I reckon.......but no plans to change anything now.