Wow, so many Background ponies here.
In any case i have no strong feelings for them. I liked Cadence premise, Princess of love or something and Shinning armor is the sterotypical knight in shining armor (yeah i know redundant).
I simply think that, as many things in the show, they have potential but the writers do not have the time, money and /or interest to explore/exploit it.
Shinnig only porpuse was to link Twi to the wedding. Cadences only purpose was to get married and thus enabling Hasbro to sell a wedding set. But it is worth noting that at least Cadeace has been consistently used as a plot device.
On a final comment i really the way they beated Chrisy at the end of ACW, i know most people did not loved the whole “love will preavail” thing, but it is MLP, a wedding episode had to end with love blasting its way through.
Why i liked it? Well Shnning armor does not saves her damsel in distress nor anyone, and Cadence does not do it either, they save the day together, with twi’s help of course. Wich diverges a little from most traditional “endings”