I probably splurged more on the travel system than a lot of the other 'big' things, and I definitely used it enough to justify it.
I had a Cosatto Giggle 2 (although didn't pay full RRP, thanks to ebay and getting one where the car seat didn't match the buggy and bassinet colouring - I didn't use them together so it didn't matter.) Car seat was used from the very beginning, until he grew out of it.
The bassinet/pram form was the most useful to me in the early days. I have dogs, so it was great to be able to walk round the park with him lying flat as he tended to nap whilst we walked. I did do some babywearing, but I had a young jumpy dog, so it was good to be able to walk with my mum and her dog and know I could quickly hand her the pram and go deal with things without carrying a newborn after an unruly mud-covered pup! The bassinet also meant I didn't need a Moses basket in my house; baby could nap in the pram and I could be anywhere in the ground floor of my house or visiting family with him, and he could sleep in the same room as me - definitely kept me sane, being able to be flexible and not tied to the house at various points of the day.
The pushchair was used the longest, and was great for those toddler years when he would get tired halfway round a walk, or if we'd gone to a zoo or country park and he was still needing naps. With the Cosatto I could tip the chair part flat(ish) and he could sleep without risk of his head lolloping forward. It could be used both forward facing and parent facing, which was a definite bonus.
One key thing to check when shopping is where the fixed wheels are and where the steerable ones are. The Cosatto had front wheel steering which was invaluable, along with the narrower front wheel so it was almost a 3-wheeler; I'd tried a friend's travel system and due to it's build, the handle changed sides, so sometimes it was front steering and sometimes back, and that was a nightmare. Back in those days Toys R Us was still open so I could go in and actually check out a real life model before ordering one online (and given how much the online retailers were undercutting prices, it's no surprise Toys R Us went under :( )
Have I sung enough praises?
Yes, babies shouldn't be left in car seats for too long, but if baby falls asleep in the car, the travel systems are great when you're just popping to the supermarket, and can pop sleeping baby straight from car to travel system without having to unbuckle and lift out and risk waking them.
Only real downside was that it was fairly chunky. I had a bigger car back then, so could take chassis and bassinet out all the time. Not sure it would be so easy with a smaller car.