F1 moved from multi-element wings, where sections spanned the entire length to what we currently have. Wider main plane, with 2-3 flaps and smaller sections above.
Previously the Front wings were scooped down shape, leaving little air to the diffuser from the front.
Now we see the middle sections hollow and I guess its abouts making the diffuser obtain slightly higher mass flow.
Returning to the main question: is it allowing closer racing??
very hard to answer this one in a straightforward manner.
Year| Car ahead | Following car
2008 | wider rear wings, Single diffuser | less wide FW,larger span area
2009 |smaller but rear wing higher,DDD | wider FW, lesser span area
2008 : the wake from the car ahead would be wider
2009: wake would be more turbulent in the center line of the car , but considering that the track width has not changed...leaving more dirty air for the car following behind...IMO
Car behind would lose much downforce, leading to understeer around corners making overtaking less possible...