If you are going to purchase one or two Nik products, you will be much better off buying the complete package. It is clear that the pricing is designed to achieve that result.
I have been using the Nik package for the last two or three years. I particularly like Silver Efex for black and white conversion, Viveza for color modifications, and Color Effects for the filters, which at first seemed a little gimmicky to me, but as I have learned what many of them do, I have been using the package a lot. I also use Define. I am not sure if the HDR program is part of the package. I am not into HDR, but I experimented with it and it was relatively easy to work with. I had purchased the package before the HDR program came out.
For context, my base program is Lightroom 4 and I do use Photoshop CS5 (waiting for 6 to be finalized). I consider myself to be working at expert level in LR and at intermediate level in Photoshop. I can mask and work with layers in Photoshop and will do so when required, but it is not where I like to spend my time. Surprisingly, I find basic color and tone adjustments difficult to make in Photoshop and much prefer LR and the Nik products.
If you do buy the package, I highly recommend Nik Software Captured: The Complete Guide to Using Nik Software's Photographic Tools by Tony L. Corbell and Joshua A. Haftel. It was published in November 2011. It is the missing manual and is essential reading. I learned a lot about the programs that wasn't evident from just using them.