Do you have an SSD installed? If so, i'm sure its fine. But without an ssd ANY mac on the market today would be brutal IMO.
If you claim otherwise, you havent used a mac with an ssd, because once you get used to it, the lags caused by a spinning drive are absolutely unbearable
It really does depend upon what using the Mac for.
My mini does have an SSD, a 60Gb Corsair that was going spare. The SSD improves boot up and Application opening times.
However my mini is on 24/7 and sits there with the EyeTV and iTunes open anyway.
All the recording/playback is done on the Drobo Pro attached. WD RE4 500Gb Disks x 8. FW800 Connection hardly the speediest either.
However putting the SSD didn't make it any quicker at what it is being used for. Machine is already up and the Apps already open.
If was opening and closing apps all the time then yes would make difference however for normal day to day operation then doesn't feel any quicker then when was the HDD. Probably if measured then would see some difference in the measured results.
If my 2009 broke then would likely but the base 1.4GHz ( My Mac Pro does the real work ) and just upgrade to 8Gb of RAM and even keep the HDD.
My use means that once booted up and running then the SSD really wouldn't make much difference.