Are these things worth it and does it really work?
Saleman at Circuit City (yes I have to buy from them because I've got a gift certificate) say they are worth the extra bucks. I thought they sounded fine but wanted some "expert" opinions.

Specifically Polk fx 300i mated with Polk RT 25i for main fronts, Polk CS245I for Center and Polk 350 subwoofer. Powered by Onkyo 474.

How's this set up? Would I get better (fuller) overall sound with RT 35i for fronts and RT15 for rears instead? I live in a relatively small apartment.

I appreciate any help.

Do the work to create a more diffuse sound state? Yes.
Should you get them? Maybe.
Are they worth more money? Not really/necessarily.

If you using Pro Logic sound then you are better off with di/bi poles to create a diffuse sound. Since the same signal is sent to both speakers your better off that way. But if your using 5.1 or 6.1 or 7.1 then it's a matter of choice. Personally I think you shouldn't. When I first upgraded from Pro Logic to Dolby Digital I replaced my dipoles with directionals (NHT SuperOnes, I have NHT's all round). If your feeding a specfic signal to the speaker then why not take advantage of it. With dipoles it's difficult to determine where the sound is coming from (which is the point).

As far as their being worth more, that's a nonsensical statement. It is true that most any dipole speaker will cost more than cheap directional speakers but so what? In my opinion you shouldn't be using dipoles at all (assuming your not using Pro Logic) so how is it worth it to pay more? And a good directional speaker will cost just as much as a good di/bipole.

For the sake of clarity, dipole and bipole are not synonymous. In a dipole design the opposing speakers are wired out of phase, while in a bipole they are in phase. A dipole will render a more diffuse soundstage than a bipole and both will provide greater dispersion than a direct design. FWIW, there are also quite a few bipole designs in use as mains.

The choice between a direct radiating design and a di/bipole for surrounds is simply a matter of preference and room environment. Both choices are valid and can yield excellent results in a 5.1 system. The idea behind using surround speakers w/ greater dispersion is to more accurately recreate the theater experience where the surround information is delivered by multiple speakers and thus more difficult to localize. Some people like a more pin-point sound, other's don't.

There's no one best approach. I use both in my system and switch between them as the mood strikes.

I agree with Audrey and would go one step further and verify the return policy so that you can exchange if you do not like your first choice.

If I get the dipole/bipole surrounds I'll be hanging them on the rear wall (definately more convenient) so they should be set to bipole. Is this correct?

But what about specific surround effects, for instance the scene in X-Men where Patrick Stewarts' voice seem to be coming from different parts of the room or in Chicken Run where the oven flames turn on in sequence all around you. Would you still be able to get those effects with the dipole/bipoles?

I guess there's a trade off with everything.

Rear wall placement for di/bipoles is generally contraindicated; dipoles are specifically designed for sidewall placement which puts the listener is in the "null" area where the sound waves cancel out.

You will still get these effects, just as you do in the theater, they just won't be as pronounced (especially w/ dipoles).