The fact that it has four buttons on it I'm going to assume what you have is a hydronic fan-coil, and not a convector, one that is muli-speed at that, which would allow you to balance room-to-room temperature by tweaking the fan speeds.
To come up with the possible solutions that really make sense would require a proper design process, starting with a room-by-room heat load calculation based (ACCA Manual-J, or I=B=R), knowledge of which rooms are zoned together (or how you'd LIKE to zone them), and the make/model of the boiler. This could be pretty straightforward or ridiculously complex, depending on what you have, and where you want to go with it. But without knowing the heat load of each room, and the operating temperature & output range of the boiler it's impossible to say how much baseboard would be required in each room, or how to balance the room-to-room temperatures on each zone.
How "attractive" is fin-tube baseboard? Most of it looks pretty crappy to me- YMMV. To a large degree it's a matter of what you're used to. Those off-white/beige sheet-metal convecting panel radiators are pretty much standard fare in Europe, and have been for at least 3-4 decades. There are more "artistic" versions (including Runtal's line) but just like prettier baseboard you pay a significant premium for it.
If you give us a ZIP code (for outside design temp purposes) and describe your windows, wall construction & insulation, and attic construction & insulation we could walk you through how to do a quick & dirty I=B=R type heat load calc, from which you could estimate the amount of baseboard/radiater it would take per room for either a cast iron boiler or condensing boiler. The boiler make/model & or it's nameplate input BTU and it's D.O.E. output BTU numbers would be important considerations too.
