For color correction, I think the choice comes down to the Elite BVP-4+ or the Sign Video / Studio 1 Proc Amp. For enhancing the detail, I think the Sign Video DR-1000 is really the only one worth it (from what I have used, see below). The BVP-4 has a 'resolution boost' setting, but it's not really the same effect as seen in the SignVideo gear. I'd guess I'd say that you have no control over the 'shape' of the sharpness with the BVP-4, where the DR-1000 gives you different ways of approaching it.
Just to state my own history -- I've only owned the Elite BVP-4+, one of the Sima color correctors, the Vidicraft Detailer III, Vidicraft AVP-100 and then some of the Sign Video / Studio 1 equipment. I should mention that the Studio 1 brand of equipment is equivalent to the Sign Video equipment. I have the Sign Video DR-1000 image enhancer and the Studio 1 PA-200 processing amp. If you are considering buying them new, try VideoGearShop.com. I got in touch Jeff Bearden there who used to work for Elite Video and he cut me a deal on a new DR-1000 for about $30 cheaper than SignVideo was selling it direct.
For color correction, the Elite BVP-4 has a huge range of color adjustment and is probably the only one of them well equipped making huge color adjustments. My collection of tapes didn't need those kinds of adjustments for the most part and I found that the SignVideo/Studio 1 equipment passes a cleaner signal than the Elite BVP-4 I procured. A lot of the 'extras' on the BVP weren't particularly useful to me. The black level restore on my unit didn't seem to work properly and ended up creating sort of an inky looking mess. The resolution boost did have an effect, but it wasn't exactly the one I desired. As a prosumer hardware color correction device though, I think it is without peer in terms of the range of adjustments. Once again, VideoGearShop was offering a new single proc amp for $410 delivered instead of $464 direct from SignVideo. I ended up buying the Studio 1 version of the Dual Proc on
eBay for around $300, which was a steal.
As far as the SignVideo gear, the luminance meter is very handy, although you need to use your eyes as well and not rely on it entirely. Actually the thing I use it most for is to ensure that my whites are not on the verge of being too hot, because it's really easy to wash the detail out of objects that are nearly white, but not quite. The extra features have often come in pretty handy for me -- the split screen and mono switch in particular. The sync button is normally pretty worthless, but I have had one occasion with one tape where having it engaged removed the slight flicker I was getting in the picture.
The best thing about the SignVideo DR-1000 image enhancer is that you have so much control over the look of the sharpness and a huge range of adjustment, far more than you'd ever need. The "Sharp" and "Detail" knobs apply two different types of sharpening algorithms and you can control the coarseness of the enhancement with the push-buttons on the front. It's not just a simple "low/high" dial or toggle switch. It's very easy to gently tweak it with the knobs and see the result in real time on the screen. You can turn it up just a little if your source is already sharp enough to your liking, but your DVD recorder shaves off some of the high frequency detail in the MPEG conversion.
The only thing that could make it an even better unit IMO would be to include an equally variable softness setting that could be applied.
I no longer have a BVP-4 on hand, but if you'd like some tests or samples done of the SignVideo stuff, I'd be happy to do it so you can take a look at how the enhancements look.
I should add -- one thing that SignVideo Proc Amp does not do is allow you to change the overall white balance of the image -- there is nothing on the unit that will perform the "Photoshop auto color" type of filter. You can shift the hue towards the red end or the green end, but if your video has a distinct cast to it, you're going to need to try another unit or software to correct that.