Hi Fred,
I haven't owned a pair of CSS rims, so this is my own analysis based on my observations and needs; happy to be corrected if wrong...
= From what I can tell, the CSS treatment adds little if any significant weight compared to an untreated rim
of the same type (i.e. CSS vs non-CSS Rigida Andras).
= If one gets the pads intended for them, the cost difference in pads is pretty negligible due to increased service life.
= There have been some reports of CSS failure, and the modality is usually extremely poor wet-weather stopping. I dunno the causality; perhaps the rim sides finally get "polished" by the brake blocks to the point where they imitate a chrome-plated steel rim. Anyway, I have seen such reports, including in posts on this Forum. I am pressed for time at the moment, but will see if I can find them for you. Bottom line: The CSS is proving to be reliable and extremely long-lived for most users. I haven't penciled it out, but I believe the cost would be worth it if one often rides in wet, gritty conditions and/or on hills. If the majority of one's riding is in dry conditions or the flats, then it might not pay. I believe it is fair to say the CSS treatment makes the rims essentially maintenance free for a very long time. I usually clean the braking track of my plain-alloy rims annually with regular use.
= A cost-effective way of going this route would be to replace the most-used rim or the one that sees the heaviest braking. I have considered going this route. Here in the States where we drive/ride of the right of the centerline, I need my left arm free to signal turns. That means my right hand controls the rear brake. The back brake is less effective than the front due to weight transfer, but it is also less likely to cause me harm if I lock it up with only one hand holding the 'bars. Therefore, the rear rim sees a lot of use -- light use -- getting feathered to a stop as I approach a stop sign or traffic light. Practically all my
intended stopping and speed modulation is done on the front wheel, thanks to the better stopping it provides. It therefore sees the most wear. If I were to replace only one rim with a CSS, it would be at the front. Rear rims last me practically forever.
The same idea would apply if you use your rear brake for the majority of your stopping needs, so yes, your strategy of replacing only the rear sounds good to me. The front wheel could continue to use a conventional rim/pad combo as before.
This is a strategy to consider if a pair is just too expensive at present.
And, finally, my comments apply only to what I've read about Rigida's proprietary CSS (Ceramic-based SuperSonic application) method. The kind employed by Mavic and others is different in application and result, with more frequent reports of cracking and flaking and with different rates of wear.
Hope this helps.
Best,
Dan.
EDIT: Ah! Here is a quick link to a discussion that might have relevance wrt potential downsides for CSS:
http://www.thorncycles.co.uk/forums/index.php?topic=2680.0 Perhaps their practical service life could be extended with a change of pad type/brand. Use the Forum Search function to check for more. I have posted some tips to getting just what you seek from Forum searches here:
http://www.thorncycles.co.uk/forums/index.php?topic=4390.0