You should not reuse a 9 year old cot mattress. I was even told that my 2 year old cot mattress that I used for DS is not suitable for the baby I am currently carrying and to replace it.
Re the rest of the stuff - depends where/how it has been stored. A pram/buggy in a garage for that amount of time is likely to be mildewy. In the attic - perhaps a bit musty and smelly.
Re clothes - I think this is a funny issue. People generally think that baby clothes HAVE to be reused however old they are (I was offered 40 year old baby clothes by MIL that BIL had as a baby ). But if a friend or relative offered YOU some clothes of theirs that they had not worn for 9 years, you would probably think it rather wierd wouldn't you? So why dress a baby like that if you have the money to get newer clothes. You can get cheap baby clothes in Asda, in sales etc AND you can choose they yourself and have the pleasure of buying something for your baby.
I think people's hearts are in the right place when they offer baby stuff around, but IMO, you have to be prepared for a refusal. I gave away some baby clothes (under 1 year old) to a family member recently and I said to her: If any of it is useful to you, then great, if not, put it in the charity shop and I think this should be the attitude of the giver. Otherwise don't give!
Usually when baby is born, friends and relatives will buy the baby some clothes as presents so you don't generally not have enough clothes for a little baby.
Anyway, no you are not being ungrateful. You are pregnant and (money permitting) it is part of it all to buy some baby things. Re the money, anyway, what I tend to do is to buy something mid priced, keep it in really nice condition and then sell it on eBay as soon as I am finished with it. That way, you get new stuff that you have chosen, but you get some of the money back after you have used it.