Cargo divider/cover, rubber mats, louder horn (i.e. OEM "Fanfare") are nice. Theft alarm is a must (if parked in public locations).
A/C is indispensable in all climate (reduces humidity in defrost) and renders resale easier.
Area 451 Cruise control, upgraded speakers, aftermarket radio with bluetooth, cargo divider/cover, EBC "green stuff" brake pads for reduced dust, sound/vibration dampening, Eiback springs if your ride isn't tight enough, K&N air filter. How about custom paint or wrap, painted or powdercoated wheels?
I didn't like the roadsterbag.
I also have EBC slotted rotors and kleenwheels.com dust shields that I like but other may care less.
Right now, I just added the all-weather rubber mats. I'd like to have the cargo cover, and I might install the extra gauges at some point, but I'm also waiting with my fingers crossed for the fog lamps to become available. Other than that, I'm very happy with my Cab.
Added all-weather floormats, flat repair kit (Nealy), jack, breaker bar + 15mm socket (all this is in the tailgate storage, wrapped in a blanket). When the 09 arrives, for it I plan to add some Wet Okole seatcovers, larger tires all around (maybe 195's) and some external graphics. Thinking about a LOUDER horn and some speakers to replace OEM ones, too. And maybe a brake light pulser . . .
I am so happy with Smart, that I sold my 08 and I am picking up a 09 next week. I bought a California Pop Top cover to keep the heat out during the summer, I used it all summer, it works great, good value at $49.00. I intend to get a Scan Gage for my 09, then maybe down the road a cold air intake and air scoop.
Okay, I have two "necessary" mods I have made: louder horn (WOLO BadBoy to replace the dinky "excuse me" horn that is stock), and cruise control (for long distance driving. Area 451 cruise).
I have a number of others I have done - both mods and add-ons: Interior trim paint, Coco floor mats, shoulder strap pads (could be considered "necessary"), "truck" lights, some decorative stuff (see my gallery), tow hitch, "periscope" lens (for seeing traffic lights when first in line), trunk organizers, etc. with more to come.
The great thing about the smart - it lends itself very well to customizations, both inexpensive and expensive, or is perfectly fine the way it is. Only you can be the judge of what becomes necessary, though I would strongly recommend floor mats of some sort - the stock carpet isn't all that robust. Whatever turns you on (to borrow from the Caddy ad) so that your car can return the favor...
I've added the DT twin tip exhaust, all weather mats, cargo divider/net and I am looking at Al & Ed's new wheels that are coming in in a couple of weeks.
I love the smart the way I got it but when I see something that calls to me-well, I gotta have it!
I agree, you have to add what you want, forget about what others say.
I have the velour floormats, however, I am considering a rubber set since the drivers side wore out fairly quickly, a vinatge Mercedes Benz hood ornament from my fathers 1971 Mercedes 170 ( His first Benny) inserted on my dashboard, and a set of Baby Moon hubcaps. I am as well thinking of the chrome dress up kit in the future. I may have a Pure, but i like it with some class.