Hmmm, a few things:
1) That is the exact BOV you want, however, you have no need for it if you have no other mods. Why do you have that but no power mods like an exhaust, mbc, or tune? The BOV is a supporting mod for running higher boost, so if you are not running higher boost, t hen it is of very little use or benefit. To reiterate, though, it is the best one you could have right now, though.
2) Trap speed is the speed you have through the traps. The traps are the last boxes at the end of the track that determine your time (and speed). The 1.8 and 1.9 are your 60 foot times, not the trap speeds. 1.8 and 1.9 aren't awful, but they are not good - not quite average even. Your stock run with a 101mph trap speed was good enough for a 13.3 or 13.4 with a good launch (~1.7 60').
3) No, the JDM MR DV did not slow you down unless you messed up the installation or messed up something in your boost system. It comes stock on Evo IXs, and they are fast as all hell, so that is very unlikely. Your cousin is definitely not right. The engine doesn't just suddenly start making 40 less whp. Yeah, wear and tear occurs, but we don't just start losing power, especially not on a car that is rarely driven. I think that either the conditions were worse (hotter, more humid, etc) or that something mechanically has gone wrong.
4) When you say "maybe buy a really good aftermarket one that'll sound really loud and perform well," you are going down the path of destruction. There is nothing good about a BOV "sounding really loud." That is pure rice and does nothing for performance. Also, the BOV you have already IS a really good BOV. There is not an aftermarket BOV that is better for your application, and sounding loud has nothing to do with performing well. The ones that are loud vent to atmosphere, and venting to atmosphere is not proper on an Evo, because we have a MAF that meters incoming air, so if you spit that air out the BOV, it throws off the air fuel ratios.
5) Since the car isn't driven much, I think you should start by putting in a fresh set of plugs. Go to Advanced Auto and buy a pack of NGK BPR7ES, then gap them to .026 and install. The install is very easy.
6) If there is no improvement, then you need to do a boost leak test. I am not sure you have the mechanical savvy to do it yourself, so if you can, find someone that knows Evos or DSMs and see if they can help you...or a local shop even. If you can do it yourself, then use this link as your guide:
http://vfaq.com/mods/ICtester.html
