maybe you could post about the riverside walk, done loads of different ones, so if you can let us know where it starts and finishes we can make comment. Kampa island is a lovely area though i must admit Lennon wall just leaves me nonplussed , 20+ years ago it was an interesting feature of the city, now just a place for tourist to write crap graffiti.
as Jason say you must go on an organised tour to see round the Municiple house but worth doing so, there are various bars ,cafes and restaurants in the building all have their merits and all are worth visiting but the American Bar for beer and Becherovka is a favourite stop for me.
As to Petrin tower area, and the cafe Republic, i was quite stunned that they allowed the cafe to be built where it is, the whole area has been completely refurbished and reorganised, nice new toilets but that cafe just ruins any views that you used to get from that area, daresay the views from the cafe will be stunning but why it was built where it is just does not make sense. there use to be places you could get snacks and drinks in the area but all gone now (well gone last time i was there) a favourite place to stop for a beer and sausage but sadly no more. It will only take 30 minutes of your time to go up and down the Tower and well worth it in my opinion. you can walk to the Strahov Monastery area in about 15 minutes from Petrin tower another lovely area and some good bars and restaurants in that area.