... well worth growing even if the seed is rather pricey.
Tomato cuttings root incredibly easily - only the Pepino melon-pear is more impressive. Try some cuttings now - it will give you confidence to dump the seed packet next year...
It's cheaper, easier and quicker (to fruit) to buy a few of the best sungold plants you can find as soon as they appear on sale in spring. You only need to buy about 1/10 of the plants you will need that year but by all means buy 1/5 for the first try, or if you want less work (though you've already saved a huge amount of time, work, heating and propagator space by using this method).
Repot generously, keep them warm, sunny & sensibly fed - when they are over 30cm cut off 5-10cm of the top shoot (and root it as a cutting) to encourage sideshoots.
Remove these side (axil) shoots when they are 5-10cm long and treat them as cuttings (leave the new top one in place so you still get one large plant).
Cuttings larger than 10cm are best rooted in water - so once you have nearly enough new plants it's worth letting one or two of the next 'generation' of sideshoots exceed 10cm - the water method will work with shoots of any size
provided you remove the lower leaves.
Any later surplus sideshoots can be dumped, so it's worth removing them as small as possible.
The key thing about this method is that the main plant will fruit only a few days later than an untouched plant (much earlier than your own seedlings unless you have really first rate heated frames).
The first generation of rooted sideshoots will fruit only a week or so later (they appear to be 'tied' to the parents' timing), even though they are smaller. The next generation only adds the same small shift (this is why it is good to move on to fewer bigger cuttings).
BTW. The best reason for stopping the plants bushing out is that airflow reduces the risk of blight by encouraging moisture to evaporate and move out. You may see Mediterranean plots packed closely but their blight problem is tiny - using Med. spacing and watering here can be fatal - apart from the fact that ours need more of the 'wan Pom sun' to make the same amount of flavour...
PS. This method works well with any tomato type you can buy as plants - the savings are the same - the only difference is that you aren't saving the dental damage done gritting your teeth to cough up the silly price of seeds.
PPS. I can buy 5 all-female cucumber plants in April for the same or less than a packet of 5 all-female seeds. Seeds of madness.