PSP or PSE?
I'm going to do something I never like to do here, and that's unleash some out-of-context personal preference.
Note that I am a daily user of Adobe products (Photoshop CS6 and Lightroom 4.1), and find them both outstanding tools as a photographer, but I am always experimenting and seeking good alternatives to these. I don't have PSE 10, just version 9, but I find it really limited compared to PSP X4. You cannot use layers in Elements unless you stay in 8-bit color depth. PSP is in this regard and in some others, just deeper than Elements it works well with 16-bit images. I have not been seriously disappointed with it except for its Raw conversion engine and some of the interface. Some excellent free Raw converters are available if that's important to you (Raw Therapee comes immediately to mind).
As to Nik products, they are good (I have Color EFX 3 and Viveza), but I think pricey for what you get. If you have a choice, I have found Topaz plug-ins to be an excellent value for the stuff I need most of the time. But, you are correct - Nik products (except for the Color EFX 3 that was included in the initial enhanced PSP X4 package) don't work with PSP.
John Setzo's message is dead on - try the trials - that will tell you much. If you haven't tried any Topaz products, do so. You may be pleasantly surprised.
As I said, dumping opinionated preferences, with no clue as to what your particular needs are, is not terribly useful, so take this all with a grain of salt. PSE might be ideal for you. Good luck in any event.