socrplyr, to be fair, you have to include cost of the TiVo in your comparison vs. the rental fees from the cable company. You're not spending $550 vs. those fees, you're spending a whopping $1,050, if you get the latest TiVo model.
So at your example rate above it would take you 4 years to break even vs. the cable company charges. And that's requiring you to pay that huge chunk all at once, instead of spreading it out over 4 years, which would not even be noticeable that you're paying the money.
And simply look on ebay at prices for tivos with lifetime on models from 4 years ago to see that you would not get much back if you were to wait that long. That would be like a series 3! Even some of the series 4 ones are going for $200-$300 on there and that's it.
I was out around $1000 for an xl4 with lifetime a few years ago and I think when I sold it I got $400 or less back, so for 1 year of use I wasted $500-$600.
I used the 1TB model, since that is what the OP said they had purchased. It is the appropriate comparable for them. An XL4 seems to be selling for between $250-$350 on eBay recently. After eBay fees, that is $200 on the low end. Not too bad for a 4+ year old model. Right now you should be able to bank (after fees, shipping, etc.) $400 for a Roamio Plus with All-in. Again, I just looked up sold ones in the last month on eBay.
Your comment about the not noticing the cable box payment is a good one. I don't operate that way. If I have any recurring purchase of more than $10 a month ($100 a year), I evaluate it. This isn't just for things you get billed for, but grocery and household purchases as well. I look at and and make sure it is necessary/wanted and if there is a cheaper alternative. I also such that if I can't pay for something up-front, I really question whether I should be getting it. I encourage anyone to evaluate their own finances in the same way. You might find that you can save $1000 a year with little change in lifestyle. For example, it drives me nuts when some of my family doesn't bother to make the yearly call to the cable company to save $30/$40/$50 a month. I don't however expect all to operate that way.
In general, a Tivo is not an amazing deal compared to a cable company's box, when it comes to direct cash outlay. It isn't really any more expensive on average either.
While I agree that it doesn't always work out in your favor (some investments do and some don't), you did choose to sell yours when you chose to sell it. You could have kept it and still probably be using it today. I presume you upgraded due to some value that the newer model had for you. Most of my family are still on TivoHDs. Why? They are paid off and they fit their needs. I did upgrade storage on a couple of them, so we did put some extra money into them. I currently am using a Roamio Pro. That I did overpay for, as I could have upgraded a Plus for $100 less (and I probably didn't even need the upgrade). That was a choice I made at the time.