Hi Ryder,
In my experience, adding a second Hi-Cap PS to a NAC 282 is certainly an upgrade. What it tends to do is further open up the sound of the NAC 282, making it even easier to hear parts of the music lower in amplitude in your favorite recordings. It also widens the perceived soundstage, and helps further the process that adding the first Hi-Cap certainly introduces. For many owners of a NAC 82 or a NAC 282 more recently, the addition of a second Hi-Cap has been a popular option. In many cases, it will represent the least expensive potential upgrade available in a Naim system, but obviously this is a general observation, not necessarily true for you.
If you are curious, and haven't already done so, you can experiment with your NAC 282 being powered only by your NAP 200 power amp and then add back your Hi-Cap DR to really gain a direct experience of what this popular upgrade offers. I would say that the first Hi-Cap is a bigger upgrade than adding a second, but the second is certainly helpful. I would not advise mixing the older Hi-Cap or even a Hi-Cap 2 with your Hi-Cap DR, you will get the best results by adding a second DR generation Hi-Cap to the NAC 282.
As noted above, some users of NAC 282's who are very strongly vinyl oriented, have found that an interesting use of a second Hi-Cap is to power a Naim phono stage with it directly- provided you use a Stageline or a Superline. So, if your budget allows it, there are multiple ways to use two Hi-Cap DR's in your system, so it is certainly a viable way to improve your system. In my experience, the only system configuration that will significantly outperform two Hi-Caps on a NAC 282 is the use of a Supercap 2, or better yet, a Supercap DR, but as noted above, this is a significantly more expensive alternative and may not be a comfortable fit for you.
Good luck in your search for better sound at home,
Bruce