I wouldn't remove your lightbar. If so, the only thing I'd suggest is going LED, which isn't cost effective, which is why I say leave it be. The Streethawk has a pretty big rotator and so long as you don't have the red rotators on a high speed motor, will do alright. As far as a bit of an upgrade for more flash, you could add the inner rotators, but I've seen a new Streethawk with that same setup with new domes and LEDs on the grille and it did a very nice job of providing effective warning. Possibly look in the vintage area for tips on how to polish the domes might help increase output of it a bit, but that's all I'd do with the bar.
Concerning your grille, if you want to go LED, I'd prefer to get a larger LED to cover the same spot. Unfortuneately, used 9x7 LEDs from the major manufacturers aren't that easy to find. I have done this upgrade on the front of a heavy rescue on a Ford 9000 chassis and an engine with a Mack CF chassis, and a pair of Whelen 900 series super linear LEDs set to a simple 90 fpm with the whole lighthead makes for a massive red wig wag seen for ages.
Now, if you can't find used 9x7 LEDs (and stay away from the gen I LEDs, not gonna give you wide angle coverage), folks have already suggested placing smaller LEDs on the grille. You can get a pair of new ones from multiple manufacturers for less than $100. I do agree with the suggestion of the pimp pods. Whatever you do, stick with two red LEDs, though. If they're four or six diode, do not split the pattern, either.
That red oscilator is just gonna keep giving you headaches. Seen plenty of them fail. Swap it out with a 7x3 LED from any major manufactuerer. Good news is you can find used deals on them in the classifieds so long as you keep checking frequently.
Concerning the micromax strobes, it kills me that E-won't mounted those facing up. Anyways, you could swap them with a 400 series LED from Whelen, but they'd be pointing up, too. I agree with leaving them as is and just adding another LED somewhere on the side of the rig where it will be perpindicular, not at an angle like the micromax is. Plenty of options, from the cheaper three or four diode LEDs from plenty of manufacturers, to something in a 7x3 LED or a 4x6 LED from any major manufacturer.
As far as a HLF, so long as you can shut it off on scene, I'd say go for it. They're cheap and effective.
I'm guessing those are the only lights you wanna replace, as I didn't see any pics of lights on the side of the body or the rear. If you're doing anymore, please post, as we'll have opinions, tips, etc to offer for the rest of the truck.