Sigma 30mm f/1.4 EX DC HSM, 0.45x multiplier, and macro filter- Good idea? Opinions?

To be more clear:
I want a wider angle than my Sigma 24mm f/3 macro, as well as a faster aperture. The minimum focusing distance of the 30mm is 40cm (or 15.7"), and since I'm not doing true macro photography, the macro filter should be just fine; all I want is to be closer to my subject in some circumstances.
The 0.45x multiplier will put me at 13.5mm (also desirable), and since it's an aspherical lens, I don't expect the multiplier to distort the image too much; just enough to give images some character.
The f/1.4 capability will allow me to shoot a lower ISO in addition to giving my subject better definition in comparison to the focus of other distractions in the frame.
I've been looking for the mythical f/1.4 super-wide lens for a while now, and this setup would only cost around $450, rather than some $2000. Would you consider this a worthy investment?
This will be used with an APS-c digital sensor.

Lens: http://www.sigmaphoto.com/...-hsm-sigma
Filters: http://www.amazon.com/...B004G88810

No.supplementary diopters (closeup filters) are fine to use for the occasional macro photographer. But cheap wide angle filters are very poor quality and will make your photos look terrible. If you want to be wider use a wider lens. If you have the 18-55 kit lens, putting closeup filters on that gives you a 28mm super-duper macro capabilities. And the picture quality will not be any worse than a wide angle filter on the Sigma.

Putting a cheap adapter on a good lens is the same as putting OK adapters on a bad lens.ideally you could try to find a 28mm macro lens. But as you already know that's a few hundred dollars.

p.s. Putting supplementary diopters on a 10mm-20mm is the widest macro I can think of. Maybe $700.

If you aren't bothering with macro photography, then you should be fine… EXCEPT that the multiplier and macro (close-up) filters will mess with quality of the shots… And there will be problems round the edges of the shots…

It is a compromise all the way around.

You have picked what is considered a "normal lens", NOT a wide angle on cropped sensored dSLR.

You have also picked another mediocre add-on lens which not only performs poorly (colour aberrations when used on a lens with it aperture wide open) and while it changes the 30 mm lens to an equivalent of a 15 mm, that equates to about a 22 mm lens on your camera when compared to the equivalent on a full frame camera.

You obviously have a good dSLR camera. Going cheap on lenses may fit your budget now, but what about the future? I would look into buying a good used wide angle zoom made by Tokina (12-24 mm comes to mind) and know you have some quality glass sitting in front of your fine camera.

Using an add-on lens like those that sell for from $40 to $60, would be like putting $30 tires on a Corvette. You spent good money on a dSLR, probably so you could increase the quality of your images. Putting second or third rate glass on it does not fit in my scheme of things when building a camera system. But maybe that's just me and all my colleagues spending too much money?

You have to decide. It should be very obvious that there's a huge different in quality between the $2, 000 and $450 investment. My scheme is to save my pennies until I can buy what I want and need.