First of all just to clear things up, Hitachi Ultravisions are not DLP technologies, they are 3 LCD projections instead. What is the main difference? DLP has a color wheel, while 3LCD projection uses 3 separate LCD chips (blue, green & red) and a prism in the middle.
Now, the symptoms you describe are very peculiar.
The “not so bright issue” could be related to the lamp, have you replaced it in the last year or more? These lamps last from 6000 hours or more, but they are not eternal.
As for the blue dots, the problem might have to do with the LCD chips; they start to burn in time duo to the heat emitted buy the light of the lamp.
If you are determend to spend money & time to repair this TV the first thing is trying to resolve the easiest issues. In this case it would be the lamp. If you change the lamp that might resolve the dim picture issue. As for the blue dots & tinted areas you’ll have to buy a new light engine, because it is very difficult to buy the colored chips separately.
Just remember when looking for a tv part, search buy part number, NOT buy model (two TVs with the exact model may contain different and not compatible parts from different generation).
The lamp is very easy to replace, the light engine on the other hand is another thing, the tricky part is remembering all the steps you take in disassembling the tv and reassembling again, in trick that I use is taking pictures of every thing I disconnect, in case I mess up.
Remember Knowing Is Half The Battle !