Converting a bike with knobby tires to slicks, or suspension to no suspension, can make sense.

I don't know that converting a flat bar bike to a road style bike makes sense. Some of the geometry is different. And they can do a lot to reduce road vibration in a road bike using computer design, that you won't get if you just do a conversion.

With the amount of money you're talking about to convert it, I just think you'd be happier in the end buying a lower cost road bike. I know I've read very good things about how bikes like the Specialized Smartweld Allez do a good job of reducing road vibration despite being aluminum, a good enough job they say it kinda makes an entry level carbon bike pointless.