I'd say definitely go for it, or one even better. There is a lot of difference between your current HU and the 7450SD (I use the 7450 myself). Firstly, if you have components up front, then you should probably amplify them. The 7450 has three RCA outputs compared to your current 1 RCA, which will let you scale up the system with up to three external amplifiers, or two if you want to use one 4 channel amp and one mono for a subwoofer, if you want to add one later. Your current HU will not allow you to fade between front and rear speakers. The 7450 also has a pretty useful media browser that allows me to quickly find a single track from over 500 that I have on the two USB's that I use.
Here are the specs of your current HU with the comparison with the 7450 below:
DEH-1550UB
CD player
LCD display (12 characters)
LED backlight
Front AUX input
Illuminated Front USB Port (1 Amp)
MP3/WMA/WAV playback
Advanced Sound Retriever
MOSFET 50 W ? 4
Supertuner? IIID FM/AM
Short-wave radio tuner
RDS
1 Set of RCA Preouts (2V)
5-Band Graphic Equalizer
Anti-Dust Design
Wired Remote Input
Display Off Mode
Detachable Face SecurityMR
Rotary Volume Control
Card-type Remote Control
DEH-7450SD
2 USB 2.0 rear inputs (1 Ext. cable included) 1Amp.
Input for SD cards
LCD Screen of 3-line full point
LED Backlight
Manual Flap Face
Advance Sound Retriever
Lever type key
Multicolor lighting (210,000 colors Independent buttons and screen)
Mosfet 50w x 4
RMS Power 22w x 4
3 RCA outputs (4v)
Super tuner III D
RDS
Specialized audio parts
5-band graphic equalizer
Detachable front (case included)
Mini jack input for remote control of OEM control (required interface)
Direct connection of iPod and iPhone (music)
Display mode turn-off for safety
Remote Control
Multi-language screen (English, Spanish, Portuguese)
Anti-dust design
I hope this helps. Good luck, whatever you choose.