I have driven 19300 Kms and am another satified user of swift DLX, not a single issue of any sort.My swift city avearge is 13-15 Kms nd highway 14-17. To improve fuel economy install iridium NGK IFR6J11 plugs, i have workshop manual of swift and it says that iridium plugs are highly recommended, they will give even more boost to the pick and performance.
It is really a superb car of suzuki and i really love its driving experience.
DLX comes with features so that you don't have to spend any money on any addons like rims, tyres as in case of other cars.I haven't spend a single ruppee on any thing so far except routine maintenance.
Regarding rear leg room space i think it is adequate for all passengers, i am 6'-1" and when i sit in rear seat i don't feel any issue.
Boot space can be increased by 60:40 split rear seat adequately.
Overall a very nice car and recommended to all.